# https://leetcode.com/problems/average-waiting-time/
from typing import List

class Solution:
    def averageWaitingTime(self, customers: List[List[int]]) -> float:
        available = customers[0][0]
        waiting = 0;
        for time in customers:
            if time[0] < available:
                waiting += available - time[0]
            else:
                available = time[0]
            waiting += time[1]
            available += time[1]
        return waiting / len(customers)