#!/usr/bin/perl
use strict;
use warnings;

while (<DATA>) {
    my @flds = split;
    if ( $flds[0].$flds[1] eq 'N/AN/A' ) {
        print "nana: $flds[2]\n";
    }
    elsif ( $flds[0] eq 'N/A' ) {
        print "na1: $flds[2]\n";
    }
    elsif ( $flds[1] eq 'N/A' ) {
        print "na2: $flds[2]\n";
    }
    else {
        print "no na: $flds[2]\n";
    }
}

__DATA__
1234 5678 no_nas_here blah blah
1234 N/A should_be_na2 blah blah
N/A 5678 must_be_na1 blah blah
N/A N/A nana