#define _USE_MATH_DEFINES
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>

using namespace std;

int main(){
	int n;
	while(cin>>n,~n){
		double a,b = n/2.0;
		do{
			a = b;
			b = a - (a*a*a-n)/(3*a*a);
		}while(abs(b*b*b-n) >= 0.00001*n);

		printf("%lf\n",b);
	}
    return 0;
}