#include<bits/stdc++.h>
using namespace std;
int main(){
  double n;
  while(cin>>n,n!=-1){
    double q=n;
    n/=2;
    while(fabs(n*n*n-q)>=0.00001*q)
      n=n-(n*n*n-q)/(3*n*n);
    printf("%.6f\n",n);
  }
}