import std.stdio;
import std.conv;
import std.string;
import std.typecons;
import std.algorithm;
import std.array;
import std.range;
import std.math;
import std.container;

void main()
{
	foreach (line; stdin.byLine) {
		auto q = line.chomp.to!double;
		if (q == -1) break;
    immutable EPS = 0.00001 * q;
    auto x = q / 2;
    while (abs(x^^3-q) >= EPS) {
      x -= (x^^3-q) / (3*x^^2);
    }
		writefln("%.12f", x);
	}
}