#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;

int main(){

	int q;
	double x;
	
	while(cin >> q){
		if(q == -1) break;
		
		x = 0.5 * q;
		while(abs(pow(x, 3) - q) >= 0.00001 * q){
			x -= (pow(x, 3) - q) / (3 * pow(x, 2));
		}
		printf("%.6lf\n", x);
	}

	return 0;

}