#include <cstdio>
#include <cstring>
#include <cstdlib> 
#include <algorithm>
 
using namespace std;

//namaega184


int main(){
	int x,y,d;scanf("%d%d%d",&x,&y,&d);
	
	if(x+y<d)printf("0\n");
	else if(x+y==d||d==0)printf("1\n");
	else{
		int ax=min(x,d),ay=min(y,d),bx=max(d,y-d),by=max(d,x-d);
		printf("%d\n",min(min(ax,ay),min(bx,by))+1);
	}
	return 0;
}