def solve(n, xs, ys):
    sx = sum(xs)
    sy = sum(ys)
    if sx < sy:
        sx, sy = sy, sx
    delta = sx - sy
    y_min = delta
    y_max = sx
    res = max(y_max - y_min + 1, 0)
    return res


def main():
    n = int(input())
    xs = []
    ys = []
    for _ in range(n - 1):
        x, y = (int(z) for z in input().split())
        xs.append(x)
        ys.append(y)
    res = solve(n, xs, ys)
    print(res)


if __name__ == "__main__":
    main()