truck

from collections import deque

liters, kilometers = deque(), deque()

for _ in range(int(input())):
    liter, kilometer = map(int, input().split())
    liters.append(liter)
    kilometers.append(kilometer)

liters_copy = liters.copy()
kilometers_copy = kilometers.copy()

gas_in_tank = 0
index = 0

while liters_copy:
    liter = liters_copy.popleft()
    kilometer = kilometers_copy.popleft()
    gas_in_tank += liter

    if gas_in_tank >= kilometer:
        gas_in_tank -= kilometer
    else:
        liters.append(liters.popleft()) # liters.rotate(-1)
        kilometers.append(kilometers.popleft()) # kilometers.rotate(-1)
        liters_copy = liters.copy()
        kilometers_copy = kilometers.copy()
        index += 1
        gas_in_tank = 0

print(index)