import java.util.*;
import java.io.*;
import java.awt.geom.*;
import static java.util.Arrays.*;

class Main{
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int x = Integer.parseInt(stdIn.next());
		int y = Integer.parseInt(stdIn.next());
		int d = Integer.parseInt(stdIn.next());
		int count = d+1;
		if(x-d<0){
			count += x-d;
		}
		if(y-d<0){
			count += y-d;
		}
		if(count<0){
			count = 0;
		}
		out.println(count);
		out.flush(); 
	}
}