#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<string>
#include<cstring>
#include<map>
#include<functional>
#include<stack>
#include<list>
#include<set>
#include<deque>
#include<climits>
using namespace std;

double abso(double n){
	if(n<0) return n*=-1;
	return n;
}

int main(){
	long long q;
	double x;
	while(cin>>q,q!=-1){
		x = q/2;
		while(abso(x*x*x-q)>=0.000001*q){
			x = x-((x*x*x-q)/(3*x*x));
		}
		printf("%.16lf\n",x);
	}
	return 0;
}