#!/usr/bin/env python
#coding:utf8

def read():
    return map(int, raw_input().split())


def work((x, y, d)):
    if x + y < d:
        print 0
    elif max(x, y) < d <= x + y:
        print x + y - d + 1
    elif min(x, y) < d <= max(x, y):
        print min(x, y) + 1
    else:
        print d + 1


if __name__ == "__main__":
    work(read())