n = int(input())
queue = []
for _ in range(n):
    data = input().split()
    num1 = data[0]
    num2 = data[1]
    queue.append(num1)
    queue.append(num2)

left_fuel = 0
index = 0
counter = 0


while True:
    liters = int(queue.pop(0))
    distance = int(queue.pop(0))

    if liters + left_fuel >= distance:
        left_fuel += liters - distance
        counter += 1
    elif liters + left_fuel < distance:
        index += 1
        counter = 0

    queue.append(liters)
    queue.append(distance)

    if counter >= n:
        print(index)
        break