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

int main()
{
  int q;
  
  while (scanf("%d", &q), q != -1){
    double x = q / 2.0;
    while (!(fabs(x * x * x - q) < q * 1e-5)){
      x = x - (x * x * x - q) / (3.0 * x * x);
    }
    printf("%f\n", x);
  }

  return (0);
}