sub iterieren {
   my $x1 = $_[0]; my $xN = 0;
   my $y1 = $_[1]; my $yN = 0;
   my $count = 0;
   for my $i (1..$_[2]){
      my $xNplus = $xN**2 - $yN**2 + $x1;
      my $yNplus = 2 * $xN * $yN + $y1;
      my $rec = $xNplus**2 + $yNplus**2;
      $xN = $xNplus;
      $yN = $yNplus;
      if ($rec > 4){$count = $i;last;}
   }
   return $count;
}