#include<iostream>
#include<vector>
#include<queue>
#include<map>
#include<stack>
#include<string>
#include<set>
#include<algorithm>
#include<cmath>
#include<limits>
#include<iomanip>
// #include<atcoder/all>
using namespace std;
// using namespace atcoder;
#define rep(i, n) for(int i = 0; i < (n); ++i)
#define ll long long
#define pii pair<int, int>
#define pll pair<ll, ll>
#define vi vector<int>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll, ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>

const int MOD = 1e9+7;
const int MOD2 = 998244353;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
const double eps = 1e-6;

template <typename T>
bool PN(T x){ if (x <= 1) return false; if (x == 2) return true; for (int i = 2; i < sqrt(x) + 1; i++) if (x % i == 0) return false; return true;}
long long Comb(int n, int i){long long ans = 1; if(i>n || i < 0) return 0; if(i == 0 || i == n) return 1; else {for(int j = 1; j <= i; ++j){ans *=(n+1-j); ans /= j; ans %= MOD;} }return ans;}
template<typename T> T gcd(T a, T b){if(b == 0) return a;else return gcd(b, a%b);}
template<typename T> T lcm(T a, T b){if(b > a) swap(a, b); T g = gcd(a, b);return a / g * b;}

template<class T> T modpow(T a, T b, T m) {
	// a^b mod m を求める
	long long p = 1, q = a;
	for (int i = 0; i < 30; i++) {
		if ((b & (1LL << i)) != 0) {
			p *= q; p %= m;
		}
		q *= q; q %= m;
	}
	return p;
}

template<class T> T Div(T a, T b, T m) {
	// a÷b の mod m での逆元を求める
	return (a * modpow(b, m - 2, m)) % m;
}

priority_queue<pii, vector<pii>, greater<pii>> pq;

void solve() {
	double n; cin >> n;
	cout << setprecision(10);
	cout << fixed;
	cout << (double)5 * (3 + sqrt(5)) / 12 * n * n * n << endl;
}

int main(void){
  solve();
  return 0;
}