chomp( (undef, $_, undef, @words) = <> );

%restore_case = map { lc, $_ } @words;

$list = join '|', map { scalar reverse lc } @words;

m/^ (?: ($list | $ | (?{ pop @submatches }) (?!) ) 
(?{ push @submatches, $^N }) )+ $/x;

pop @submatches;

print join ' ', map { $restore_case{ scalar reverse } } @submatches