And to add in general use of situations like this (for min and max) use 'each' first. Modified version from above.

my %hashName = (a => -1, b => -2, c => -3);
my $max = $hash{each %hashName};
$_ > $max and $max = $_ for values %hashName;
print $max;
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And you'll the scalar set as one in the hash in the beginning.