sub r{
	print"? @_\n";
	<>*2-$_[0];
}
sub w{
	exit!print"! @_\n";
}
$|=1;
$n=<>;
$a=r(1);
$a^r($n-1)||w(2,$n-1);
$r=$n;
(r($m=$l+$r>>1)*$a||w($m*2<$n?($m+1,$n):(1,$m)))>0?$l:$r=$m while 1;