perl -F: -al0ne '$i||=1;/^n/&&print$i;!/^u/&&print$F[1];/^$/&&$i++&&print$/'

##</code><code>##

LINE: while (defined($_ = <ARGV>)) {
    chomp $_;
    @F = split(/:/, $_, 0);
    $i ||= 1;
    print $i if /^n/;
    print $F[1] if not /^u/;
    print $/ if /^$/ and $i++;
}

##</code><code>##

perl '-F: ' -al0ne '!/^u/&&print qq($F[1] );/^$/&&print$/'