Buggy python submission (verdict: Time Limit Exceeded):
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

memo = [
    [0, 1, 1],
    [1,10,9],
    [2,11,9],
    [3,4,3],
    [4,13,9],
    [5,14,9],
    [6,5,3],
    [7,16,9],
    [8,17,9],
    [9,2,1],
]


def main():
    m = int(input())
    dc = [[int(i) for i in input().split()] for _ in range(m)]
    s = []
    ans = 0
    for i in range(m):
        d = dc[i][0]
        c = dc[i][1]
        ans += c // memo[d][2] * memo[d][1]
        if d == 9:
            ans -= 2
            s.append([d, 1])
        else:
            s.append([d, (c % memo[d][2])])
    if not s:
        print(ans)
        return

    t = s[0][0]
    s[0][1] -= 1
    for i in range(len(s)):
        if s[i][0] == 1:
            ans += s[i][1]
            t += s[i][1]
            if t > 9:
                ans += 1
                t = t % 10 + t // 10
            continue
        while s[i][1]:
            s[i][1] -= 1
            ans += 1
            t += s[i][0]
            if t > 9:
                ans += 1
                t = t % 10 + t // 10

    print(ans)

main()


Fixed submission:
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

def main():
    m = int(input())
    ans = 0
    a = 0
    for i in range(m):
        d, c = map(int, input().split())
        ans += c
        a += d * c
    print(ans + (a - 1) // 9 - 1)

main()

Buggy python submission (verdict: Time Limit Exceeded):
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

memo = [
    [0, 1, 1],
    [1,10,9],
    [2,11,9],
    [3,4,3],
    [4,13,9],
    [5,14,9],
    [6,5,3],
    [7,16,9],
    [8,17,9],
    [9,2,1],
]


def main():
    m = int(input())
    dc = [[int(i) for i in input().split()] for _ in range(m)]
    s = []
    ans = 0
    for i in range(m):
        d = dc[i][0]
        c = dc[i][1]
        ans += c // memo[d][2] * memo[d][1]
        if d == 9:
            ans -= 2
            s.append([d, 1])
        else:
            s.append([d, (c % memo[d][2])])
    if not s:
        print(ans)
        return

    t = s[0][0]
    s[0][1] -= 1
    for i in range(len(s)):
        while s[i][1]:
            s[i][1] -= 1
            ans += 1
            t += s[i][0]
            if t > 9:
                ans += 1
                t = t % 10 + t // 10

    print(ans)

main()


Fixed submission:
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

def main():
    m = int(input())
    ans = 0
    a = 0
    for i in range(m):
        d, c = map(int, input().split())
        ans += c
        a += d * c
    print(ans + (a - 1) // 9 - 1)

main()

Buggy python submission (verdict: Runtime Error):
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

memo = [
    [0, 1, 1],
    [1,10,9],
    [2,11,9],
    [3,4,3],
    [4,13,9],
    [5,14,9],
    [6,5,3],
    [7,16,9],
    [8,17,9],
    [9,2,1],
]


def main():
    m = int(input())
    dc = [[int(i) for i in input().split()] for _ in range(m)]
    s = []
    ans = 0
    for i in range(m):
        d = dc[i][0]
        c = dc[i][1]
        ans += c // memo[d][2] * memo[d][1]
        if d == 9:
            ans -= 2
            s.append(d)
        else:
            s.extend([d] * (c % memo[d][2]))

    t = s[0]
    for i in range(1, len(s)):
        ans += 1
        t += s[i]
        if t > 9:
            ans += 1
            t = t % 10 + t // 10

    print(ans)

main()


Fixed submission:
from collections import Counter

mod = 1000000007


def inverse(a):
    return pow(a, mod - 2, mod)


def usearch(x, a):
    lft = 0
    rgt = len(a) + 1
    while rgt - lft > 1:
        mid = (rgt + lft) // 2
        if a[mid] <= x:
            lft = mid
        else:
            rgt = mid
    return lft

def main():
    m = int(input())
    ans = 0
    a = 0
    for i in range(m):
        d, c = map(int, input().split())
        ans += c
        a += d * c
    print(ans + (a - 1) // 9 - 1)

main()