def main():
    N = int(input())
    A = [0] * N
    B = [0] * N
    for i in range(1,N):
        A[i], B[i] = map(int, input().split())
    
    sumA = sum(A)
    sumB = sum(B)

    ans = 0
    for B1 in range(sumA+1):
        A1 = B1 + sumB - sumA
        if A1 >= 0:
            ans += 1

    print(ans)
if __name__ == "__main__":
    main()