#! /usr/bin/perl -wl

use strict;

while( <DATA> ) {
    chomp;
    print "$_ ",  /^(19[5-9]\d|20([0-4]\d|50))$/ ? 'ok' : 'nok';
}

__DATA__
1949
1950
1951
1999
2000
2001
2010
2049
2050
2051
2102
22102
19534
19080
20010