#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define repf(i, j, n) for (int i = (j); i < (n); i++)
#define repr(i, n) for (int i = (n)-1; i >= 0; i--)

signed main() {
  int n;
  cin >> n;



  
  cout << 15 * n / 10 << endl;
}