import heapq

def minimumAverage(customers):
    customers.sort()
    n = len(customers)
    i = 0
    current_time = 0
    waiting_time = 0
    h = []

    while i < n or h:
        # Add all custoemrs with arrival time less or equal to current time so that no customer that arrives later is processed, as that is not valid.
        while i < n and customers[i][0] <= current_time:
            heapq.heappush(h, (customers[i][1], customers[i][0]))
            i += 1

        # From the clients whose arrival time is less than the current time, extract the one whose pizza has the least preparation time.
        if h:
            prep_time, arrival_time = heapq.heappop(h)
            current_time += prep_time
            waiting_time += current_time - arrival_time

        # In case there are no customers to process, move to next customer. :)
        else:
            current_time = customers[i][0]

    return waiting_time // n