Buggy python submission (verdict: Runtime Error):
# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub
from pprint import pprint

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62-1

def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(N, CD):
    ans = 0
    r = 0
    C = []
    for i in range(10):
        s = i
        s += i
        c = 1
        p = 1
        while s != i:
            s += i
            c += 1
            p += 1
            if s >= 10:
                s = s % 10 + s // 10
                p += 1
        C.append((i, c+1, p))
    C[0] = (0, 1, 1)

    ans = 0
    rem = []
    for d, c in CD:
        if d == 0:
            ans += c
            continue
        _, dc, dv = C[c]
        while c >= dc:
            v = c // dc
            ans += v * dv
            c = c % dc + v
        for _ in range(c):
            rem.append(d)

    while len(rem) > 1:
        a = rem.pop()
        b = rem.pop()
        c = a + b
        ans += 1
        if c >= 10:
            c = c % 10 + c // 10
            ans += 1
        rem.append(c)

    return ans


def main():
    N = read_int()
    CD = [read_int_n() for _ in range(N)]
    print(slv(N, CD))


if __name__ == '__main__':
    main()


Fixed submission:
# -*- coding: utf-8 -*-
import bisect
import heapq
import math
import random
import sys
from collections import Counter, defaultdict, deque
from decimal import ROUND_CEILING, ROUND_HALF_UP, Decimal
from functools import lru_cache, reduce
from itertools import combinations, combinations_with_replacement, product, permutations
from operator import add, mul, sub
from pprint import pprint

sys.setrecursionlimit(100000)
input = sys.stdin.readline
INF = 2**62-1

def read_int():
    return int(input())


def read_int_n():
    return list(map(int, input().split()))


def read_float():
    return float(input())


def read_float_n():
    return list(map(float, input().split()))


def read_str():
    return input().strip()


def read_str_n():
    return list(map(str, input().split()))


def error_print(*args):
    print(*args, file=sys.stderr)


def mt(f):
    import time

    def wrap(*args, **kwargs):
        s = time.time()
        ret = f(*args, **kwargs)
        e = time.time()

        error_print(e - s, 'sec')
        return ret

    return wrap


@mt
def slv(N, CD):
    S = sum(map(lambda x: x[0] * x[1], CD))
    D = sum(map(lambda x: x[1], CD))
    return D - 1 + (S-1) // 9


def main():
    N = read_int()
    CD = [read_int_n() for _ in range(N)]
    print(slv(N, CD))

    # N = 100
    # CD = [[random.randint(0, 9), random.randint(1, 10000)] for _ in range(N)]
    # print(N)
    # print(CD)
    # print(slv(N, CD))


if __name__ == '__main__':
    main()