my %seen;

while (<>) {
   chomp;
   my ($p,$c) = split /:/;

   ++$seen{$p} if !$seen{$p};
   $p .= " $seen{$p}" if $seen{$p} > 1;

   ++$seen{$c};
   $c .= " $seen{$c}" if $seen{$c} > 1;

   print("$p:$c\n");
}