#include 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 #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; }