#!/usr/bin/perl
use strict;

my %idcount;

while (<>) {
    if ( /,CO(\d+)\s/ ) {
        $idcount{$1}++
    }
}
my ( $highest ) = sort { $idcount{$b} <=> $idcount{$a} } keys %idcount;
my $total = 0;
$total += $_ for ( values %idcount );

print "Highest count was for group CO$highest, with $idcount{$highest} out of $total users\n";