Welcome to Perl!

First, rather than rewriting your looping and logic, let's just cover the expression for checking alternatives and I think you can work out the rest as part of your own experimentation. You can do it like this (parens added for clarity):

($input ne 'good') && ($input ne 'bad') && ($input ne 'iffy')
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You may not be ready for regular expressions quite yet, but they provide another approach to matching alternatives

! ( $input =~ /good|bad|iffy/ )
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You can read that =~ bit as "input matches good or bad or iffy" in the way we idiomatically mean that in English. Negating that can also be done all in one as this:

$input !~ /good|bad|iffy/
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Best of luck