Please save yourself some effort in future and use  <code> ... </code> tags; please see Markup in the Monastery and Writeup Formatting Tips.

my $n=$number/10000;
$n=~s/\..*//;

The purpose of the  s/\..*// substitution seems to to be to truncate a number to an integer. The built-in function int exists for this purpose
    my $n = int($number/10000);
or one could simply put a useinteger; statement at the beginning of one's code and all arithmetic operations thereafter will be integer operations:

use warnings;
use strict;
use integer;
...
my $n = $number/10000;
...
my $n = $number/1000;
...
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