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

int main(void) {

  int q;
  double x_n;

  while(1) {

    scanf("%d",&q);

    if(q==-1) break;

    x_n=(double)q/2.0;

    while(fabs(x_n*x_n*x_n-q)>=0.00001*q) x_n=x_n-(x_n*x_n*x_n-q)/(3*x_n*x_n);

    printf("%lf\n",x_n);

  }

  return 0;

}
 