n = int(input())
A = [0]*n
B = [0]*n
for i in range(n-1):
    A[i+1],B[i+1] = map(int,input().split())

AS = sum(A)
BS = sum(B)

ans = 0
for a in range((n+2)*10**4):
    b = a+AS-BS

    if b >= 0 and a <= BS and b <= AS:
        ans += 1
print(ans)