Truck Tour

""" Truck Tour"""
# judge
# https://judge.softuni.org/Contests/Practice/Index/1831#4

from collections import deque

gas_station = int(input())
liters, kilometers = deque(), deque()
current_gas_station = 0

for i in range(gas_station):
    liter, kilometer = map(int, input().split())
    liters.append(liter)
    kilometers.append(kilometer)
if sum(kilometers) <= sum(liters):
    while liters:
        current_liter = liters.popleft()
        current_kilometer = kilometers.popleft()

        if current_liter < current_kilometer:
            current_gas_station += 1
            liters.append(current_liter)
            kilometers.append(current_kilometer)
        else:
            remaining_liters = current_liter - current_kilometer
            if kilometers:
                liters[0] += remaining_liters
            else:
                break

print(current_gas_station)


"""
input:

5
22 5
14 10
52 7
21 12
36 9

output:
0

"""