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


int main() {
int a;
cin >> a;
int b;
  if (a>4)
  {
   a = a - 4;
    if (a % 2 == 0) {
   b = (a / 2) * 10 + 4;
    }
     else if(a % 2 == 1) 
     {b = ((a + 1)/2)* 10 +4 +1;
     }
    cout << b;
  }
   else if (a <= 4)
   { b = (a / 2) * 2;
    if (a % 2 == 1)
    {b +=3;}
    cout << b;
   }
}