#include <iostream>
#include <algorithm>
using namespace std;
int main(){
  int a,b,s;
  cin>>a>>b>>s;
  if(s==1){
    if(a>0){
      cout<<a<<endl;
    } else if(a==0){
      cout<<2<<endl;
    }
    return 0;
  }
  int x,y,z;
  x=abs(a-s);
  y=abs(b-s);
  if(x<=y){
    if(x>=s){
      z=a;
    } else {
      z=x+s;
    }
  } else {
    if(y>=s){
      z=b-1;
    } else {
      z=y+s-1;
    }
    z+=a;
  }
  cout<<z<<endl;
  return 0;
}