This is a programming game. it cannot be used. please advise.

This is a programming game, there is no way to pass, please advise https://paiza.jp/poh/ando/challenge/5eb06c7e/ando16
This is a programming game website. can someone use the "eye Belt? Is the last line of the eye.
Although it is in Japanese, I think it is better to understand the problem.
After code debugging, I went to the first CASE of the final Test and encountered an error.

Reply to discussion (solution)

Fgets (STDIN );
Fgets (STDIN );
$ H = explode ('', trim (fgets (STDIN )));
Fgets (STDIN );
$ O = array_diff (explode ('', trim (fgets (STDIN), $ h );
Sort ($ o );
Echo empty ($ o )? 'None': implode ('', $ o );
?>