import sys
input = sys.stdin.readline

N = int(input())
A, B = [], []

for _ in range(N-1):
    Ai, Bi = map(int, input().split())
    A.append(Ai)
    B.append(Bi)

ans = 0
SA, SB = sum(A), sum(B)

for A1 in range(SB+1):
    B1 = SA+A1-SB
    
    for i in range(N-1):
        if A[i]>B1+SB-B[i]:
            break
    else:
        ans += 1

print(ans)