#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  int x, y, d; cin >> x >> y >> d;
  int a = -1;
  int lb = 0, rb = x;
  while( lb <= rb ){
    int mid = ( lb + rb ) / 2; // >> 1;
    if( mid + y >= d )
      a = mid, lb = mid + 1;
    else
      rb = mid - 1;
  }
  if( a == -1 ) cout << 0 << endl, exit( 0 );
  int b = -1;
  lb = 0, rb = x;
  while( lb <= rb ){
    int mid = ( lb + rb ) / 2; // >> 1;
    if( mid + y >= d )
      b = mid, rb = mid - 1;
    else
      lb = mid + 1;
  }
  cout << b - a + 1 << endl;
  return 0;
}