Placing your angle operator inside of double quotes treats it as a literal "less than" and "greater than" symbol...

Instead try:

chomp($operator = <STDIN>);
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with the extra chomp there to get rid of your record input separator, (newline by default) so that you have control over where your newlines go when you print.

Also if you want to add $a and $b instead of printing them out literally, try

print $a + $b, "\n";
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Cheers,
Kristina