Sorry -- you may have wanted to know where your code went wrong. It's here:

$interessa =~ s/$um/\.$um/;
[download]

The "$um" just contains "000", and when you apply this to a value like "80000", it matches the first three zeroes. You needed something like this:

$interessa =~ s/$um\b/\.$um/;
[download]

But you also needed to cut down on the amount work you're doing in general.