my $thisKey;
my $lastLine = <>;
my $lastKey = '';  # first line is header, so always print
while (<>) {
	if (/(.*?)\t.*/) {
		$thisKey = $1
	} else {
		warn "bad data: $_ had no tab\n";
	}
	if ($thisKey ne $lastKey) {
		print $lastLine;
	}
	$lastLine = $_;
	$lastKey = $thisKey;
}
print $lastLine;