#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
int main(){
  double x,q;
  while(  cin >> q ){
    if(q == -1.0)break;
    x = q/2;
    while(fabs(pow(x,3) - q) >= 0.00001*q )x = x - (pow(x,3) - q)/(3*pow(x,2));
    printf("%.10f\n",x);
  }
  return 0;
}