import std;
import core.bitop;
import core.checkedint;
import core.time;

const c = 2.18169499062491237350;

void main() {
	const n = readln.chomp.to!int;
	writeln(format("%.12f", c * (n ^^ 3)));
}

pragma(inline)
string yes(const bool b) pure @nogc nothrow @safe {
	return b ? "Yes" : "No";
}