#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
#define int ll
#define _FastIO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define pii pair<int , int>
#define pb push_back
#define F first
#define S second
const int mod = 1e9 + 7;
const int MAXX = 1e6 + 5;

int t , n;
int a[MAXX];
string s;

signed main()
{
    _FastIO;
    cout.precision(12);
    cin >> n;
    n *= 3;
    long double ans = sqrt(n * 1.00) * 1.00;
    ans = ans * 1.0 / 36 * 1.0;
    n /= 3;
    ans *= n;
    long double l = sqrt(n * 1.00);
    ans = ans * 1.0 * l * 1.0;
    cout << fixed << ans << endl;
    return 0;
}