#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001



int main(){
	
	double t = 15;
	t += 5.0 * sqrt(5.0);
	t /= 12.0;
	
	double n;
	cin>>n;
	
	t *= n * n * n;
	cout<<fixed<<setprecision(10)<<t<<endl;
	
	return 0;
}