#include <iostream>
#include <sstream>
#include <algorithm>
#include <cstdio>
#include <string>
#include <vector>
#include <cmath>

//AOJ0080
#define rep(x,to) for(int x=0;x<to;x++)
#define rep2(x,from,to) for(int x=from;x<to;x++)

using namespace std;


int main(void){

double q;
	
	while( cin >> q){
		if(q==-1 || cin.eof()) break;
		double x = q / 2;
		while(1){
			x = x - (x*x*x - q)/(3*x*x);
			if(abs(x*x*x-q) < 0.00001*q) break;
		}
		printf("%.6f\n",x);
	}
	return 0;
	
}