#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
using ll=long long;
using ld=double;
ld pie=3.14159265359;
ll mod=998244353;
long long inf=100000000000000001;
int main(){
    ld n;
    cin >> n;
    cout << setprecision(100) << (5.0*(3.0+sqrt(5))*n*n*n)/12.0 << endl;
}