#include <bits/stdc++.h>
using namespace std;


int main() {
int a;
cin >> a;
int b;
  if (a>4)
  {
   a = a - 4;
   b = (a / 2) * 10 + 4;
     if (a % 2 == 1)
     { b += 3;
     }
    cout << b;
  }
   else
   { b = (a / 2) * 2;
    if (a % 2 == 1)
    {b +=3;}
    cout << b;
   }
}