truck turns

from collections import deque
num_petrol_pumps = int(input())
gas_tank = 0
list_of_gas_stations = deque()
station_num = 0
for _ in range(num_petrol_pumps):
    info = [int(x) for x in input().split()]
    list_of_gas_stations.append(info)

while list_of_gas_stations:
    current_pump = list_of_gas_stations.popleft()
    litters = current_pump [0]
    distance = current_pump[1]
    available_fuel = gas_tank + litters

    if available_fuel < distance:
        list_of_gas_stations.append(current_pump)
        station_num += 1
    else:
        litters_left = (available_fuel - distance)
        gas_tank = litters_left

print(station_num)