my %b_lookup;
for (<$file_b>) {
	my ($num, $data) = split(/ /, $_, 2);
	$b_lookup{$num} = "$num $data";
}

for (<$file_a>) {
	my ($num, $data) = split(/ /, $_, 2);
	
	if (exists $b_lookup{$num}) {
		print $file_c $b_lookup{$num}."\n";
	}
	else {
		print $file_c "$_\n";
	}
}