#!/usr/bin/perl -w

use strict;

my $date;
my $lastdate = '';

while(<DATA>){
   $date = $_;
   if (($lastdate ne $date) && ($lastdate ne '')){
      # print $lastdate report here
      print "$.    $_";
   }
   $lastdate = $date;
}
__DATA__
10
10
10
11
11
11
12
12
12