#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

ll N;

int main() {
  cin >> N;
  double S = (double)(((1 + 6) * 6) / 2) / 6;
  cout << fixed << setprecision(6) << S * N << endl;
  return 0;
}