#!/usr/bin/perl

use strict;
use warnings;

my %index;
my @data = qw/1 2 3 4 3 4 5 1 11 11 11 11 11 3/;
my $filename;

for (@data) {
	if ($index{$_}) {
		$filename =  $_ . $index{$_};
		$index{$_}++;
	}
	else {
		$filename = $_;
		$index{$_} = 'a';
	}
	print "Your filename is $filename.\n";
}

##</code><code>##

Your filename is 1.
Your filename is 2.
Your filename is 3.
Your filename is 4.
Your filename is 3a.
Your filename is 4a.
Your filename is 5.
Your filename is 1a.
Your filename is 11.
Your filename is 11a.
Your filename is 11b.
Your filename is 11c.
Your filename is 11d.
Your filename is 3b.