get_match_count($s1,$s2);

sub get_match_count {

    my ( $k, $l ) = @_;
    return 0 if $k eq $l;

    my $len       = length($k);
    my $num_match = 0;

    for ( my $i = 0; $i < $len; $i++ ) {
        next if ( substr( $k, $i, 1 ) eq 'N' 
                        and 
                  substr( $l, $i, 1 ) eq 'N' );
        ++$num_match if substr( $k, $i, 1 ) eq substr( $l, $i, 1 );
    }

    print "$num_match\n";
    return $num_match;
}