This condition never happens:

last if ($_ eq '');
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So your while loop just keeps going and going. Their test harness is expecting you to return a sorted list of numbers, but your script is just sitting there waiting for more input.

Your input loop should be something like:

chomp(my $count = <>);

my @numbers;
for (1 .. $count) {
   chomp(my $line = <>);
   die if $line < 1 || $line > 1_000_000;
   push @numbers, $line;
}
[download]