#include <iostream>
using namespace std;
int main(){
    int x,y,d;cin>>x>>y>>d;
    //y=$(y)とy+x=d
    //(d-y,y)
    //(x,d-x)
    if(x < d-y || y < d-x){
        cout << 0 << endl;
    }else{
        cout << min(x-(d-y),d+1) << endl;
    }
}