//Third Root
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

int main(){
  ll q;
  while(cin>>q){
    if(q==-1)break;
    double x=q/2.0;
    while(fabs(pow(x, 3.0)-q)>=0.00001*q){
      x=x-(pow(x, 3.0)-q)/(3.0*x*x);
    }
    printf("%.8f\n", x);
  }
  return 0;
}