Shared code

import sys

input = sys.stdin.readline


def solve(n, tasks):
    # we can see that deadline doesnt matter cuz we always have to do the task
    # python optimise:
    arr = sorted(map(lambda x: (x[0] << 32) + x[1], tasks))
    ans = 0
    curr_time = 0
    for x in arr:
        duration, deadline = x >> 32, x % (1 << 32)
        curr_time += duration
        ans += deadline - curr_time
    print(ans)


def main():
    n = int(input())
    tasks = [list(map(int, input().split())) for _ in range(n)]
    solve(n, tasks)


main()