Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = n
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            lazy[2*i] = (lazy[2*i] + v) % mod
            data[2*i-1] = (data[2*i-1] + v) % mod
            data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) #% mod
                data[R-1] = (data[R-1] + x) #% mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) #% mod
                data[L-1] = (data[L-1] + x) #% mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return (data[N0+l-1]) % mod



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = n
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            lazy[2*i] = (lazy[2*i] + v) % mod
            data[2*i-1] = (data[2*i-1] + v) % mod
            data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) % mod
                data[R-1] = (data[R-1] + x) % mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) % mod
                data[L-1] = (data[L-1] + x) % mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = n
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            lazy[2*i] = (lazy[2*i] + v) % mod
            data[2*i-1] = (data[2*i-1] + v) % mod
            data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) % mod
                data[R-1] = (data[R-1] + x) % mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) % mod
                data[L-1] = (data[L-1] + x) % mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = n
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            if lazy[2*i-1] + v >= mod:
                lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            else:
                lazy[2*i-1] += v
            # lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            if lazy[2*i] + v >= mod:
                lazy[2*i] = (lazy[2*i] + v) % mod
            else:
                lazy[2*i] += v
            # lazy[2*i] = (lazy[2*i] + v) % mod 
            if data[2*i-1] + v >= mod:
                data[2*i-1] = (data[2*i-1] + v) % mod
            else:
                data[2*i-1] += v           
            # data[2*i-1] = (data[2*i-1] + v) % mod
            if data[2*i] + v >= mod:
                data[2*i] = (data[2*i] + v) % mod
            else:
                data[2*i] += v                  
            # data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) % mod
                data[R-1] = (data[R-1] + x) % mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) % mod
                data[L-1] = (data[L-1] + x) % mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())
    def debug(x): print(x, file=sys.stderr)
    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = n
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            lazy[2*i] = (lazy[2*i] + v) % mod
            data[2*i-1] = (data[2*i-1] + v) % mod
            data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) % mod
                data[R-1] = (data[R-1] + x) % mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) % mod
                data[L-1] = (data[L-1] + x) % mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys


def main():
    mod = 998244353
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())
    def debug(x): print(x, file=sys.stderr)
    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = 2 * n + 1
    
    # N: 処理する区間の長さ
    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] = (lazy[2*i-1] + v) % mod
            lazy[2*i] = (lazy[2*i] + v) % mod
            data[2*i-1] = (data[2*i-1] + v) % mod
            data[2*i] = (data[2*i] + v) % mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)
        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] = (lazy[R-1] + x) % mod
                data[R-1] = (data[R-1] + x) % mod
            if L & 1:
                lazy[L-1] = (lazy[L-1] + x) % mod
                data[L-1] = (data[L-1] + x) % mod
                L += 1
            L >>= 1; R >>= 1
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i + l, min(i + r + 1, n + 1), p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    # inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def mi():     return map(int, input().split())
    def lmi():    return list(map(int, input().split()))
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    

    n, k = mi()
    intervals = [tuple(mi()) for _ in range(k)]
    N = 2 * n + 1
    
    # N: 処理する区間の長さ
    INF = 2**63-1

    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] += v
            lazy[2*i] += v
            #
            lazy[2*i-1] %= mod
            lazy[2*i] %= mod
            data[2*i-1] += v
            data[2*i] += v
            #
            data[2*i-1] %= mod
            data[2*i] %= mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)

        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] += x
                data[R-1] += x
                # 
                lazy[R-1] %= mod
                data[R-1] %= mod
            if L & 1:
                lazy[L-1] += x
                data[L-1] += x
                # 
                lazy[L-1] %= mod
                data[L-1] %= mod
                L += 1
            L >>= 1; R >>= 1
        # for i in ids:
        #     data[i-1] = min(data[2*i-1], data[2*i])

    # # 区間[l, r)内の最小値を求める
    # def query(l, r):
    #     propagates(*gindex(l, r))
    #     L = N0 + l; R = N0 + r

    #     s = INF
    #     while L < R:
    #         if R & 1:
    #             R -= 1
    #             s = min(s, data[R-1])
    #         if L & 1:
    #             s = min(s, data[L-1])
    #             L += 1
    #         L >>= 1; R >>= 1
    #     return s
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        # p = query(i, i+1)
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i+l, i+r+1, p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    

    n, k = mi()
    intervals = [lmi() for _ in range(k)]
    N = 2 * n + 1
    
    # N: 処理する区間の長さ
    INF = 2**31-1

    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] += v
            lazy[2*i] += v
            #
            lazy[2*i-1] %= mod
            lazy[2*i] %= mod
            data[2*i-1] += v
            data[2*i] += v
            #
            data[2*i-1] %= mod
            data[2*i] %= mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)

        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] += x
                data[R-1] += x
                # 
                lazy[R-1] %= mod
                data[R-1] %= mod
            if L & 1:
                lazy[L-1] += x
                data[L-1] += x
                # 
                lazy[L-1] %= mod
                data[L-1] %= mod
                L += 1
            L >>= 1; R >>= 1
        for i in ids:
            data[i-1] = min(data[2*i-1], data[2*i])

    # 区間[l, r)内の最小値を求める
    def query(l, r):
        propagates(*gindex(l, r))
        L = N0 + l; R = N0 + r

        s = INF
        while L < R:
            if R & 1:
                R -= 1
                s = min(s, data[R-1])
            if L & 1:
                s = min(s, data[L-1])
                L += 1
            L >>= 1; R >>= 1
        return s
    
    # [l] を求める
    def get(l):
        propagates(*gindex(l, l+1))
        return data[N0+l-1]



    update(0, 1, 1)
    for i in range(n):
        # p = query(i, i+1)
        p = get(i)
        # print(p)
        for l, r in intervals:
            if i + l < n:
                update(i+l, i+r+1, p)
    
    # print(query(n-1, n))
    print(get(n-1))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    

    n, k = mi()
    intervals = [lmi() for _ in range(k)]
    N = 2 * n + 1
    
    # N: 処理する区間の長さ
    INF = 2**31-1

    LV = (N-1).bit_length()
    N0 = 2**LV
    data = [0]*(2*N0)
    lazy = [0]*(2*N0)

    def gindex(l, r):
        L = (l + N0) >> 1; R = (r + N0) >> 1
        lc = 0 if l & 1 else (L & -L).bit_length()
        rc = 0 if r & 1 else (R & -R).bit_length()
        for i in range(LV):
            if rc <= i:
                yield R
            if L < R and lc <= i:
                yield L
            L >>= 1; R >>= 1

    # 遅延伝搬処理
    def propagates(*ids):
        for i in reversed(ids):
            v = lazy[i-1]
            if not v:
                continue
            lazy[2*i-1] += v
            lazy[2*i] += v
            #
            lazy[2*i-1] %= mod
            lazy[2*i] %= mod
            data[2*i-1] += v
            data[2*i] += v
            #
            data[2*i-1] %= mod
            data[2*i] %= mod
            lazy[i-1] = 0

    # 区間[l, r)にxを加算
    def update(l, r, x):
        *ids, = gindex(l, r)
        propagates(*ids)

        L = N0 + l; R = N0 + r
        while L < R:
            if R & 1:
                R -= 1
                lazy[R-1] += x
                data[R-1] += x
                # 
                lazy[R-1] %= mod
                data[R-1] %= mod
            if L & 1:
                lazy[L-1] += x
                data[L-1] += x
                # 
                lazy[L-1] %= mod
                data[L-1] %= mod
                L += 1
            L >>= 1; R >>= 1
        for i in ids:
            data[i-1] = min(data[2*i-1], data[2*i])

    # 区間[l, r)内の最小値を求める
    def query(l, r):
        propagates(*gindex(l, r))
        L = N0 + l; R = N0 + r

        s = INF
        while L < R:
            if R & 1:
                R -= 1
                s = min(s, data[R-1])
            if L & 1:
                s = min(s, data[L-1])
                L += 1
            L >>= 1; R >>= 1
        return s


    update(0, 1, 1)
    for i in range(n):
        p = query(i, i+1)
        # print(p)
        for l, r in intervals:
            update(i+l, i+r+1, p)
    print(query(n-1, n))


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    

    class BucketRAQ:
        """ 1 点に対する質問クエリ、区間に対する加算クエリ (Range Add Query)"""

        def __init__(self, total_size: int, chunk_size: int=512):
            if total_size < chunk_size:
                chunk_size = total_size
                # raise ValueError(f"BucketRAQ.__init__(): chunk size should be <= total_size. got total: {total_size}, chunk: {chunk_size}")
            self.size = total_size    # 列の長さ
            self.chunk_size = chunk_size    # 何個ごとに bucket として分割されるか
            self.chunk_num = (total_size + chunk_size - 1) // chunk_size    # bucket の個数
            self.bucket_add = [0] * self.chunk_num
            self.data = [0] * self.size
        

        def _parent(self, data_ind: int) -> int:
            """データインデックスからバケットのインデックスを得る"""
            return data_ind // self.chunk_size
        
        def _child(self, bucket_ind: int) -> Tuple[int, int]:
            """バケットインデックスから管轄データのインデックス範囲 [l, r) を得る"""
            l = bucket_ind * self.chunk_size
            r = min((bucket_ind + 1) * self.chunk_size, self.size)
            return l, r
        
        
        def build(self, L: Sequence[Num]) -> None:
            """ O(n) で初期配列 L に対応したバケットを構築する"""
            for i, num in enumerate(L):        
                self.data[i] = num
        
        
        def range_add(self, l: int, r: int, num: Num) -> None:
            """ O(lgn) で [l,r) の区間に num を足す"""
            if not (0 <= l <= r <= self.size):
                raise IndexError(f"Bucket_RAQ.range_add(): invalid slices (0 <= l <= r <= {self.size} is required). got l: {l}, r: {r}")
            for bucket_ind in range(self.chunk_num):
                # 現在の bucket の管轄範囲は [i, j)
                i, j = self._child(bucket_ind)
                if r <= i:
                    break
                if j <= l:
                    continue
                # 対象区間が bucket を包み込んでいる時
                if l <= i and j <= r:
                    self.bucket_add[bucket_ind] += num
                    self.bucket_add[bucket_ind] %= mod    # mod
                # 部分的にかぶっている時、現在のバケットに含まれている対象区間の部分区間のみ計算する
                else:
                    for data_ind in range(max(l, i), min(r, j)):
                        self.data[data_ind] += num
                        self.data[data_ind] %= mod    # mod


        def get(self, i: int) -> Num:
            """ O(1) で L[i] を得る"""
            return (self.bucket_add[self._parent(i)] + self.data[i]) % mod    # mod
    

    n, k = mi()
    intervals = [lmi() for _ in range(k)]
    bucket = BucketRAQ(2 * n + 1)
    bucket.data[0] = 1
    for i in range(n):
        p = bucket.get(i)
        # print(p)
        # print(bucket.data)
        for l, r in intervals:
            bucket.range_add(i+l, i+r+1, p)
    print(bucket.get(n-1))
        

        


if __name__ == "__main__":
    main()


Fixed submission:
#!/usr/bin/env python3

import sys
from typing import Any, Callable, Deque, Dict, List, Mapping, Optional, Sequence, Set, Tuple, TypeVar, Union
# import time
# import math, cmath
# import numpy as np
# import scipy.sparse.csgraph as cs            # csgraph_from_dense(ndarray, null_value=inf), bellman_ford(G, return_predecessors=True), dijkstra, floyd_warshall
# import random                                # random, uniform, randint, randrange, shuffle, sample
# import string                                # ascii_lowercase, ascii_uppercase, ascii_letters, digits, hexdigits
# import re                                    # re.compile(pattern) => ptn obj; p.search(s), p.match(s), p.finditer(s) => match obj; p.sub(after, s)
# from bisect import bisect_left, bisect_right # bisect_left(a, x, lo=0, hi=len(a)) returns i such that all(val<x for val in a[lo:i]) and all(val>-=x for val in a[i:hi]).
# from collections import deque                # deque class. deque(L): dq.append(x), dq.appendleft(x), dq.pop(), dq.popleft(), dq.rotate()
# from collections import defaultdict          # subclass of dict. defaultdict(facroty)
# from collections import Counter              # subclass of dict. Counter(iter): c.elements(), c.most_common(n), c.subtract(iter)
# from datetime import date, datetime          # date.today(), date(year,month,day) => date obj; datetime.now(), datetime(year,month,day,hour,second,microsecond) => datetime obj; subtraction => timedelta obj
# from datetime.datetime import strptime       # strptime('2019/01/01 10:05:20', '%Y/%m/%d/ %H:%M:%S') returns datetime obj
# from datetime import timedelta               # td.days, td.seconds, td.microseconds, td.total_seconds(). abs function is also available.
# from copy import copy, deepcopy              # use deepcopy to copy multi-dimentional matrix without reference
# from functools import reduce                 # reduce(f, iter[, init])
# from functools import lru_cache              # @lrucache ...arguments of functions should be able to be keys of dict (e.g. list is not allowed)
# from heapq import heapify, heappush, heappop # built-in list. heapify(L) changes list in-place to min-heap in O(n), heappush(heapL, x) and heappop(heapL) in O(lgn).
# from heapq import _heapify_max, _heappop_max, _siftdown_max
# from heapq import nlargest, nsmallest        # nlargest(n, iter[, key]) returns k-largest-list in O(n+klgn).
# from itertools import count, cycle, repeat   # count(start[,step]), cycle(iter), repeat(elm[,n])
# from itertools import groupby                # [(k, list(g)) for k, g in groupby('000112')] returns [('0',['0','0','0']), ('1',['1','1']), ('2',['2'])]
# from itertools import starmap                # starmap(pow, [[2,5], [3,2]]) returns [32, 9]
# from itertools import product, permutations  # product(iter, repeat=n), permutations(iter[,r])
# from itertools import combinations, combinations_with_replacement
# from itertools import accumulate             # accumulate(iter[, f])
# from operator import itemgetter              # itemgetter(1), itemgetter('key')
# from fractions import Fraction               # Fraction(a, b) => a / b ∈ Q. note: Fraction(0.1) do not returns Fraciton(1, 10). Fraction('0.1') returns Fraction(1, 10)



def main():
    Num = Union[int, float]
    # mod = 1000000007                # 10^9+7
    mod = 998244353
    inf = float('inf')              # sys.float_info.max = 1.79e+308
    # inf = 2 ** 63 - 1             # (for fast JIT compile in PyPy) 9.22e+18
    sys.setrecursionlimit(10**6)    # 1000 -> 1000000
    def input():  return sys.stdin.readline().rstrip()
    def ii():     return int(input())
    def isp():    return input().split()
    def mi():     return map(int, input().split())
    def mi_0():   return map(lambda x: int(x)-1, input().split())
    def lmi():    return list(map(int, input().split()))
    def lmi_0():  return list(map(lambda x: int(x)-1, input().split()))
    def li():     return list(input())
    def debug(x): print(x, file=sys.stderr)
    # def _heappush_max(h, item): h.append(item); _siftdown_max(h, 0, len(h)-1)
    
    
    n, k = mi()
    L = [lmi() for _ in range(k)]
    dp = [0] * n
    dp[0] = 1
    acc = [0] * (n + 1)    # acc[i] = sum(dp[:i])
    acc[1] = 1
    for i in range(1, n):
        s = 0
        for l, r in L:
            # sum(dp[i-r:i-l+1]) を足していく
            s = (s + acc[max(0, i - l + 1)] - acc[max(0, i - r)]) % mod
        dp[i] = s
        acc[i+1] = (acc[i] + dp[i]) % mod
        # debug(dp)
        # debug(acc)
    print(dp[n-1])


if __name__ == "__main__":
    main()