N = int(input())
A_sum, B_sum = 0, 0
X = []
for i in range(N - 1):
    A, B = map(int,input().split())
    X.append([A, B])
    A_sum += A
    B_sum += B


ans = 0
for nb in range(A_sum, -1, -1):
    na = B_sum + nb - A_sum
    if na < 0 or nb < 0:
        continue
    for a, b in X:
        if (B_sum + nb - b) < a:
            break

        if (A_sum + na - a) < b:
            break
    else:
        ans += 1


print(ans)