#include <stdio.h>
#include <math.h>
#include <float.h>
long double PerfectRootEstimate( long double X )
{
   long double Guess;
   long double Test;
   long double Min = 0.69220062755534635386542199718278976149L;
   long double Max = 1546.0e0L; /* Max^Max = LDBL_MAX */
   int n;
   for ( n = 0; n < 16; n++ )
   {
      Guess = ( Min + Max ) * 0.5e0L;
      Test = powl( Guess, Guess );
      if ( Test > X )
         Max = Guess;
      else
         Min = Guess;
   }
   return Guess;
}
int main()
{
   printf("%30.20LeL\n", PerfectRootEstimate( 27.0e0L ) );
   printf("%30.20LeL\n", PerfectRootEstimate( 10000000000.0e0L ) );
   printf("%30.20LeL\n", PerfectRootEstimate( LDBL_MAX ) );
   return 0;
}