#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

int main() {
  int L; cin >> L;
  double ans = 0.0481125224324688137111 * L * L;
  cout << fixed << setprecision(15) << ans << endl;
  return 0;
}