#include <iostream>
#include <cmath>

using namespace std;

int main(int argc, char **argv)
{
	float x, q;
	while(cin >> q){
		if(q == -1){
			break;
		}
		x = q/2;
		while(fabs(x*x*x-q) > 0.00001*q){
			x = x-(x*x*x-q)/(3*x*x);
		}
		printf("%.6f\n", x);
	}
	
	return 0;
}