#include<bits/stdc++.h> #include <atcoder/all> using namespace atcoder; using mint=modint998244353; using namespace std; using ll=long long; using ul=unsigned long long; int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}; int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1}; using Graph=vector<vector<int>>; int main(){ double N; cin>>N; cout<<fixed<<setprecision(10)<<5.0*(3+sqrt(5))*N*N*N/12<<endl; }