use strict;
use warnings;
use 5.010;

while (<DATA>){
    chomp;
    # note the string IS always odd
    if ((length $_) % 2 < 1){
        print "Not OK $_ (unbalanced)\n";
        next;
    }
    if (($_=~/./g)[0,(int((length $_)/2)-1),-1]~~[qw(x x x)]){
      print "$_\t\tOK\n";
    }
    else {
       print "NOT OK $_\n";
    }

}