use feature 'say';
$|=1;
$n=<>;
$z="z"x$n;
say "? ","a"x$n;
$o=<>;
for$i(0..$n-1){
	for$c("b".."y"){
		say "? ","a"x$i,$c,"a"x($n-$i-1);
		$r=<>;
		if($r>$o){
			substr($z,$i,1)=$c;
			last;
		}
		if($r<$o){
			substr($z,$i,1)="a";
			last;
		}
	}
}
say "! $z";