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

int main()
{
	double N;
	cin >> N;
	double S = 5 * sqrt(3) * N * N;
	double r = (3 * sqrt(3) + sqrt(15)) * N / 12;
	cout << setprecision(18) << S * r / 3 << endl;
	return 0;
}