Just to start, you probably want to split on ";" instead of a ","

Then, run your program with the debugger to learn about what is happening.
That should give you a good start toward both learning what Perl is doing as well as how to troubleshoot.
perl -d your_program_name.pl

Following compiles and gives you a start

#!/usr/bin/perl
use strict;
use warnings;
 
my $count = 0;
while (my $line = <DATA>) {
  chomp $line;
  my @fields = split ";" , $line;
  my $rows = $fields[2];
  $count++;
  }

print "$count\n";


__DATA__

13645722;20110327203202.0Z;20140211204731.0Z
14947374;20110327203202.0Z;20140220135320.0Z
15962660;20110327203156.0Z;20131106113716.0Z
17480884;20110327212821.0Z;20131211143804.0Z
13054554;20110327203141.0Z;20131205162959.0Z
[download]

Hope that is helpful...