#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    long double N;
    cin >> N;
    cout << setprecision(18) << N*N*N*2.18169499062491237350 <<endl;

    return 0;
}