#include <iostream>
#include <iomanip>
#include <cstdint>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	
	uint32_t N;
	cin >> N;

	const uint32_t squared_N = N * N;
	const uint64_t cubed_N = squared_N * static_cast<uint64_t>(N);

	cout << fixed << setprecision(12) << cubed_N * 2.18169499062491237350 << '\n';
	return 0;
}