#include <stdio.h>
#include <math.h>

int main(){
  double q, x;
  while(scanf("%lf", &q) && q != -1){
    x = q / 2.0;
    while(fabs(x*x*x -q) > 0.00001 * q) x -= (x*x*x - q) / (3 *x*x);
    printf("%.6f\n", x);
  }
  return 0;
}