#include <iostream>
#include <algorithm>
#include <stdlib.h>
#include <string>
using namespace std;






int main() {
int x,y,d;
cin>>x>>y>>d;
if(y>x){
int k=x;
x=y;
y=k;
}//x>=y

if(d>x+y) cout<<"0"<<endl;
else if(x<d) cout<<x+y-d+1<<endl;
else if(y<d) cout<<y+1<<endl;
else  cout<<d+1<<endl;



	return 0;
}