#include <cstdio>
#include <cstdlib>
#include <cmath>
const static double EPS = 1e-5;

double cube( double x ) {
  return x * x * x;
}

int main() {

  while( 1 ) {
    int q;
    scanf( "%d", &q );
    if( q == -1 ) { break; }

    double x;
    for(
        x = q / 2.0;
        fabs( cube( x ) - q ) >= q * EPS;
        x = x - ( cube( x ) - q ) / ( 3 * x * x )
       );

    printf( "%.6f\n", x );

  }
  return EXIT_SUCCESS;
}