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

int main(int argc, char **argv)
{
   long double x;
   long double k;
   char pszString[256] = "2";

   if ( argc < 2 )
   {
      printf( "Enter a number to find square root of:" );
      fgets( pszString, sizeof( pszString ), stdin );
      puts( pszString );
  }
   else
      strncpy( pszString, argv[1], sizeof( pszString ) );

   k = atof( pszString );
   x = powl( k, 1.0e0L/3.0e0L ) * 1.00001; /* form estimate correct to 5 digits */
   x += 3*(-x*x*x + k)*x*(2*x*x*x+k)/(10*x*x*x*x*x*x +16*x*x*x*k +k*k);
   printf("answer = %30.20LeL\nx      = %30.20LeL\n", powl( k, 1.0e0L/3.0e0L ), x );
   return 0;
}