#include <iostream>
#include <utility>
#include <algorithm>
#include <string>
#include <vector>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <cstdlib>

typedef long long int ll;


using namespace std;

int q;
double x;

double f(){
	return x*x*x-q;
}
double df(){
	return 2*x*x;
}

double calc(){
	x=q/2.0;
	while(1){
		if((fabs(f())>-0.00001*q&&fabs(f())<0.00001*q)){
			break;
		}
		x=(x*df()-f())/df();
	}
	return x;
}

int main(){
	while(1){
		cin>>q;
		if(q==-1)break;
		printf("%.15lf\n", calc());
	}
}