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

#define EPS 1e-6

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