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

bool eq(double x, double q){
    return abs(x*x*x-q) < 0.00001*q;
}

int main(){
    double n;
    while( cin >> n, n != -1 ){
        double x = n/2;
        while( true ){
             x = x - (x*x*x-n)/(3*x*x);
             if( eq(x, n) ) break;
         }
        cout << x << endl;
    }
} 