package main

import (
	"fmt"
)

func main() {
	var x, y, d, ans int64
	fmt.Scanln(&x, &y, &d)

	if x+y < d {
		fmt.Println(0)
		return
	}

	if x >= d {
		if y >= d {
			ans = d
		} else {
			ans = y
		}
	} else {
		diff := d - x
		if y-diff > d {
			ans = d
		} else {
			ans = y - diff
		}
	}
	fmt.Println(ans + 1)
}