#include <iostream>
using namespace std;

int main()
{
  int in,base,base_ans=-1;
  cin>>in;
  for(base=2; base<100; base++){
    if(in-base == 7){
      base_ans = base;
      break;
    }
  }
  if(base_ans<=7){
    base_ans = -1;
  }
  cout<<base_ans<<endl;
  return 0;
}