#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
 
int main()
{
  int q;
  while (cin >> q, q != -1){
    double x = q / 2.0;
    while (fabs(pow(x, 3) - q) >= 0.00001 * q){
      x = x - (pow(x, 3) - q) / (3 * x * x);
    }
    printf("%f\n", x);
  }
  return (0);
}