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

int main(){
  double q,x,EPS;
  while(true){
    cin >> q;
    if(q == -1)break;
    EPS = 0.00001*q;
    x = q/2;
    while(fabs(q-pow(x,3)) > EPS){
      x = x-(pow(x,3)-q)/(pow(x,2)*3);
    }
    printf("%.6f\n",x);
  }
  return 0;
}