def main():
    x, y, d = map(int, input().split())
    if d > (x+y):
        print(0)
        return

    if d <= min(x, y):
        print(d+1)
        return
    if d <= max(x, y):
        print(min(x, y)+1)
        return
    print(min(x, y) + 1 - (d - max(x, y)))


if __name__ == "__main__":
    main()