print "Please enter a numerical grade:";
$num=<>;     
chomp($num);     
%num_letter = (
        "0" => "F",
        "60" => "D",
        "70" => "C",
        "80" => "B",
        "90" => "A",
        "100" => "A+",
        );
print $num_letter{"$num"};
}