from _collections import deque
petrol_n = int(input())
full_circle = []
tail = deque()
have_fuel = 0

while petrol_n > 0:
    income = [int(x) for x in input().split()]
    full_circle.append(income[0])
    tail.append(income[0])
    tail.append(income[1])
    petrol_n -= 1

for j in range(0, len(full_circle)):
    have_fuel = tail[0]
    for i in range(1, len(tail)):
        if i % 2 == 0:
            have_fuel += tail[i]
        else:
            if  have_fuel < tail[i]:
                tail.append(tail[0])
                tail.append(tail[1])
                tail.popleft()
                tail.popleft()
                have_fuel = 0
                break
            else:
                have_fuel -= tail[i]
    if i == len(tail)-1:
        print(j)
        quit()