#include<iostream>
#include<cmath>
#include<cstdio>

using namespace std;

long long in;
long double judge;

int getketa(int in){
  int sum = 0;
  while(in){
    in/=10;
    sum++;
  }
  return sum;
}

void make(){
  //int keta = getketa(in);
  judge = 0.1 * in;
  judge++;
  //for(int i = 0; i < 5+keta; i++) judge *= 0.1;
  //judge += 0.00001;
  // cout << judge << endl;
}
int main(){

  while(cin >> in){
    if(in == -1) break;
    make();
    long double x = in/2;
    while(1){
      x = 2*x/3+in/x/x/3;
      if(fabs(x*x*x - in)*10*10*10*10*10 < judge) break;
    }
    printf("%.6Lf\n",x);
  }
  return 0;
}