from sys import stdin


def main():
    input = lambda: stdin.readline()[:-1]
    N = int(input())
    AB = [tuple(map(int, input().split())) for _ in [0] * (N - 1)]

    asum, bsum = 0, 0
    for a, b in AB:
        asum += a
        bsum += b
    if asum < bsum:
        print(abs(asum - bsum))
    elif asum > bsum:
        print(1)
    else:
        print(asum + 1)


main()