Buggy python submission (verdict: Time Limit Exceeded):
N, K = [int(_) for _ in input().split()]
LR = [[int(_) for _ in input().split()] for _ in range(K)]
mod = 998244353


class LazySegmentTree():
    def __init__(self, array, f, g, h, ti, ei):
        """
        Parameters
        ----------
        array : list
            to construct segment tree from
        f : func
            binary operation of the monoid
            T x T -> T
            T is dat
        g : func
            binary operation of the monoid
            T x E -> T
            T is dat, E is laz
        h : func
            binary operation of the monoid
            E x E -> T
            E is laz
        ti : T
            identity element of T
        ei : E
            identity element of E
        """
        self.f = f
        self.g = g
        self.h = h
        self.ti = ti
        self.ei = ei
        self.height = height = len(array).bit_length()
        self.n = n = 2**height
        self.dat = dat = [ti] * n + array + [ti] * (n - len(array))
        self.laz = [ei] * (2 * n)
        for i in range(n - 1, 0, -1):  # build
            dat[i] = f(dat[i << 1], dat[i << 1 | 1])

    def reflect(self, k):
        dat = self.dat
        ei = self.ei
        laz = self.laz
        g = self.g
        return self.dat[k] if laz[k] is ei else g(dat[k], laz[k])

    def evaluate(self, k):
        laz = self.laz
        ei = self.ei
        reflect = self.reflect
        dat = self.dat
        h = self.h
        if laz[k] is ei:
            return
        laz[(k << 1) | 0] = h(laz[(k << 1) | 0], laz[k])
        laz[(k << 1) | 1] = h(laz[(k << 1) | 1], laz[k])
        dat[k] = reflect(k)
        laz[k] = ei

    def thrust(self, k):
        height = self.height
        evaluate = self.evaluate
        for i in range(height, 0, -1):
            evaluate(k >> i)

    def recalc(self, k):
        dat = self.dat
        reflect = self.reflect
        f = self.f
        while k:
            k >>= 1
            dat[k] = f(reflect((k << 1) | 0), reflect((k << 1) | 1))

    def update(self, a, b, x):  # set value at position [a, b) (0-indexed)
        thrust = self.thrust
        n = self.n
        h = self.h
        laz = self.laz
        recalc = self.recalc
        a += n
        b += n - 1
        l = a
        r = b + 1
        thrust(a)
        thrust(b)
        while l < r:
            if l & 1:
                laz[l] = h(laz[l], x)
                l += 1
            if r & 1:
                r -= 1
                laz[r] = h(laz[r], x)
            l >>= 1
            r >>= 1
        recalc(a)
        recalc(b)

    def set_val(self, a, x):
        n = self.n
        thrust = self.thrust
        dat = self.dat
        laz = self.laz
        recalc = self.recalc
        ei = self.ei
        a += n
        thrust(a)
        dat[a] = x
        laz[a] = ei
        recalc(a)

    def query(self, a, b):  # result on interval [a, b) (0-indexed)
        f = self.f
        ti = self.ti
        n = self.n
        thrust = self.thrust
        reflect = self.reflect
        a += n
        b += n - 1
        thrust(a)
        thrust(b)
        l = a
        r = b + 1
        vl = vr = ti
        while l < r:
            if l & 1:
                vl = f(vl, reflect(l))
                l += 1
            if r & 1:
                r -= 1
                vr = f(reflect(r), vr)
            l >>= 1
            r >>= 1
        return f(vl, vr)


#RSQ and RAQ
array = [0] + [1] + [0] * 2 * N
f = lambda a, b: a if a else b
g = lambda a, b: (a + b) % mod
h = lambda a, b: (a + b) % mod
ti = 0
ei = 0

LST = LazySegmentTree(array=array, ti=ti, ei=ei, f=f, g=g, h=h)
for x in range(1, N):
    v = LST.query(x, x + 1)
    for l, r in LR:
        LST.update(x + l, x + r + 1, v)
ans = LST.query(N, N + 1)
print(ans)


Fixed submission:
N, K = [int(_) for _ in input().split()]
LR = [[int(_) for _ in input().split()] for _ in range(K)]
mod = 998244353


class SegmentTree():
    def __init__(self, array, f, ti):
        """
        Parameters
        ----------
        array : list
            to construct segment tree from
        f : func
            binary operation of the monoid
        ti : 
            identity element of the monoid
        """
        self.f = f
        self.ti = ti
        self.n = n = 2**(len(array).bit_length())
        self.dat = dat = [ti] * n + array + [ti] * (n - len(array))
        for i in range(n - 1, 0, -1):  # build
            dat[i] = f(dat[i << 1], dat[i << 1 | 1])

    def update(self, p, v):  # set value at position p (0-indexed)
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = v
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_right(self, p, v):  # apply operator from the right side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(dat[p], v)
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_left(self, p, v):  # apply operator from the left side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(v, dat[p])
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def query(self, l, r):  # result on interval [l, r) (0-indexed)
        f, ti, n, dat = self.f, self.ti, self.n, self.dat
        vl = vr = ti
        l += n
        r += n
        while l < r:
            if l & 1:
                vl = f(vl, dat[l])
                l += 1
            if r & 1:
                r -= 1
                vr = f(dat[r], vr)
            l >>= 1
            r >>= 1
        return f(vl, vr)


st = SegmentTree([0] + [1] + [0] * N, lambda x, y: x + y, 0)
for i in range(2, N + 1):
    v = 0
    for l, r in LR:
        il = max(0, i - r)
        ir = max(0, i - l + 1)
        v += st.query(il, ir)
        v %= mod
    st.update(i, v)
ans = st.query(N, N + 1)
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
N, K = [int(_) for _ in input().split()]
LR = [[int(_) for _ in input().split()] for _ in range(K)]
mod = 998244353


class LazySegmentTree():
    def __init__(self, array, f, g, h, ti, ei):
        """
        Parameters
        ----------
        array : list
            to construct segment tree from
        f : func
            binary operation of the monoid
            T x T -> T
            T is dat
        g : func
            binary operation of the monoid
            T x E -> T
            T is dat, E is laz
        h : func
            binary operation of the monoid
            E x E -> T
            E is laz
        ti : T
            identity element of T
        ei : E
            identity element of E
        """
        self.f = f
        self.g = g
        self.h = h
        self.ti = ti
        self.ei = ei
        self.height = height = len(array).bit_length()
        self.n = n = 2**height
        self.dat = dat = [ti] * n + array + [ti] * (n - len(array))
        self.laz = [ei] * (2 * n)
        for i in range(n - 1, 0, -1):  # build
            dat[i] = f(dat[i << 1], dat[i << 1 | 1])

    def reflect(self, k):
        dat = self.dat
        ei = self.ei
        laz = self.laz
        g = self.g
        return self.dat[k] if laz[k] is ei else g(dat[k], laz[k])

    def evaluate(self, k):
        laz = self.laz
        ei = self.ei
        reflect = self.reflect
        dat = self.dat
        h = self.h
        if laz[k] is ei:
            return
        laz[(k << 1) | 0] = h(laz[(k << 1) | 0], laz[k])
        laz[(k << 1) | 1] = h(laz[(k << 1) | 1], laz[k])
        dat[k] = reflect(k)
        laz[k] = ei

    def thrust(self, k):
        height = self.height
        evaluate = self.evaluate
        for i in range(height, 0, -1):
            evaluate(k >> i)

    def recalc(self, k):
        dat = self.dat
        reflect = self.reflect
        f = self.f
        while k:
            k >>= 1
            dat[k] = f(reflect((k << 1) | 0), reflect((k << 1) | 1))

    def update(self, a, b, x):  # set value at position [a, b) (0-indexed)
        thrust = self.thrust
        n = self.n
        h = self.h
        laz = self.laz
        recalc = self.recalc
        a += n
        b += n - 1
        l = a
        r = b + 1
        thrust(a)
        thrust(b)
        while l < r:
            if l & 1:
                laz[l] = h(laz[l], x)
                l += 1
            if r & 1:
                r -= 1
                laz[r] = h(laz[r], x)
            l >>= 1
            r >>= 1
        recalc(a)
        recalc(b)

    def set_val(self, a, x):
        n = self.n
        thrust = self.thrust
        dat = self.dat
        laz = self.laz
        recalc = self.recalc
        ei = self.ei
        a += n
        thrust(a)
        dat[a] = x
        laz[a] = ei
        recalc(a)

    def query(self, a, b):  # result on interval [a, b) (0-indexed)
        f = self.f
        ti = self.ti
        n = self.n
        thrust = self.thrust
        reflect = self.reflect
        a += n
        b += n - 1
        thrust(a)
        thrust(b)
        l = a
        r = b + 1
        vl = vr = ti
        while l < r:
            if l & 1:
                vl = f(vl, reflect(l))
                l += 1
            if r & 1:
                r -= 1
                vr = f(reflect(r), vr)
            l >>= 1
            r >>= 1
        return f(vl, vr)


#RSQ and RAQ
array = [(0, 1)] + [(1, 1)] + [(0, 1)] * 2 * N
f = lambda a, b: (a[0] + b[0], a[1] + b[1])
g = lambda a, b: ((a[0] + a[1] * b) % mod, a[1])
h = lambda a, b: (a + b) % mod
ti = (0, 0)
ei = 0

LST = LazySegmentTree(array=array, ti=ti, ei=ei, f=f, g=g, h=h)
for x in range(1, N):
    v = LST.query(x, x + 1)[0]
    for l, r in LR:
        LST.update(x + l, x + r + 1, v)
ans = LST.query(N, N + 1)
print(ans[0])


Fixed submission:
N, K = [int(_) for _ in input().split()]
LR = [[int(_) for _ in input().split()] for _ in range(K)]
mod = 998244353


class SegmentTree():
    def __init__(self, array, f, ti):
        """
        Parameters
        ----------
        array : list
            to construct segment tree from
        f : func
            binary operation of the monoid
        ti : 
            identity element of the monoid
        """
        self.f = f
        self.ti = ti
        self.n = n = 2**(len(array).bit_length())
        self.dat = dat = [ti] * n + array + [ti] * (n - len(array))
        for i in range(n - 1, 0, -1):  # build
            dat[i] = f(dat[i << 1], dat[i << 1 | 1])

    def update(self, p, v):  # set value at position p (0-indexed)
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = v
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_right(self, p, v):  # apply operator from the right side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(dat[p], v)
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_left(self, p, v):  # apply operator from the left side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(v, dat[p])
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def query(self, l, r):  # result on interval [l, r) (0-indexed)
        f, ti, n, dat = self.f, self.ti, self.n, self.dat
        vl = vr = ti
        l += n
        r += n
        while l < r:
            if l & 1:
                vl = f(vl, dat[l])
                l += 1
            if r & 1:
                r -= 1
                vr = f(dat[r], vr)
            l >>= 1
            r >>= 1
        return f(vl, vr)


st = SegmentTree([0] + [1] + [0] * N, lambda x, y: x + y, 0)
for i in range(2, N + 1):
    v = 0
    for l, r in LR:
        il = max(0, i - r)
        ir = max(0, i - l + 1)
        v += st.query(il, ir)
        v %= mod
    st.update(i, v)
ans = st.query(N, N + 1)
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
N, K, *LR = [int(_) for _ in open(0).read().split()]
L = LR[::2]
R = LR[1::2]
mod = 998244353
dp = [0] * 3 * N
dp[1] = 1
for s in range(1, N):
    for l, r in zip(L, R):
        for d in range(l, r + 1):
            dp[s + d] += dp[s]
            dp[s + d] %= mod
print(dp[N])


Fixed submission:
N, K = [int(_) for _ in input().split()]
LR = [[int(_) for _ in input().split()] for _ in range(K)]
mod = 998244353


class SegmentTree():
    def __init__(self, array, f, ti):
        """
        Parameters
        ----------
        array : list
            to construct segment tree from
        f : func
            binary operation of the monoid
        ti : 
            identity element of the monoid
        """
        self.f = f
        self.ti = ti
        self.n = n = 2**(len(array).bit_length())
        self.dat = dat = [ti] * n + array + [ti] * (n - len(array))
        for i in range(n - 1, 0, -1):  # build
            dat[i] = f(dat[i << 1], dat[i << 1 | 1])

    def update(self, p, v):  # set value at position p (0-indexed)
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = v
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_right(self, p, v):  # apply operator from the right side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(dat[p], v)
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def operate_left(self, p, v):  # apply operator from the left side
        f, n, dat = self.f, self.n, self.dat
        p += n
        dat[p] = f(v, dat[p])
        while p > 1:
            p >>= 1
            dat[p] = f(dat[p << 1], dat[p << 1 | 1])

    def query(self, l, r):  # result on interval [l, r) (0-indexed)
        f, ti, n, dat = self.f, self.ti, self.n, self.dat
        vl = vr = ti
        l += n
        r += n
        while l < r:
            if l & 1:
                vl = f(vl, dat[l])
                l += 1
            if r & 1:
                r -= 1
                vr = f(dat[r], vr)
            l >>= 1
            r >>= 1
        return f(vl, vr)


st = SegmentTree([0] + [1] + [0] * N, lambda x, y: x + y, 0)
for i in range(2, N + 1):
    v = 0
    for l, r in LR:
        il = max(0, i - r)
        ir = max(0, i - l + 1)
        v += st.query(il, ir)
        v %= mod
    st.update(i, v)
ans = st.query(N, N + 1)
print(ans)