use strict;
use warnings;

my ( %masked, @results );

while ( my $line = <STDIN> ) {
    my ($ip) = $line =~ / (\d+ \. \d+ \. \d+ \. \d+) /x
      or next;

    my $mask = pack 'C3', split /\./, $ip;

    if ( $masked{$mask} ) {
        if ( not $masked{$mask}{repeat} ) {
            $masked{$mask}{ip} =~ s{ \d+ \z }{0/24}x;
            $masked{$mask}{repeat} = 1;
        }
    }
    else {
        $masked{$mask} = {
            ip => $ip,
        };
        push @results, $masked{$mask};
    }
}

print $_->{ip}, "\n" for @results;