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

ll N;

int main() {
  cin >> N;
  long double ans = (long double)N * N * N * (long double)(2.18169499062491237350);
  cout << fixed << setprecision(20) << ans << endl;
  return 0;
}