gistfile1.pl

use 5.14.2;
use warnings;
use Data::Dump;
my %value;

open my $C, '<', $ARGV[0] || die;
while (<$C>) {
        chomp;
        my @line = split /\t/;
        $value{$line[0]} = $line[1];
}
close $C;

open my $D, '<', $ARGV[1] || die;
while (<$D>) {
        chomp;
        my @line = split /\t/;
        $value{$line[0]} += $line[1];
}
close $D;

for (sort {$a <=> $b} keys %value) {
        say join "\t", ($_, $value{$_}/2);
}