#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <set>
#include <random>
#include <iomanip>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)

template<class T>
using vi = vector<T>;

template<class T>
using vii = vector<vi<T>>;

template<class T>
using viii = vector<vii<T>>;

using pii = pair<int, int>;
using tii = tuple<ll, int, int>;

int main()
{
    double v = 2.18169499062491237350;
    double n;
    cin >> n;
    cout << fixed << setprecision(12) << n * n * n * v << endl;
    return 0;
}