func main()
	var ok: int :: 0
	var ng: int :: 10 ^ 9 + 1
	while((ok - ng).abs() > 1)
		var mid: int :: (ok + ng) / 2
		do cui@print("? \{mid}")
		do cui@flush()
		if(cui@inputInt() = 1)
			do ok :: mid
		else
			do ng :: mid
		end if
	end while
	var ans: int :: ok
	do cui@print("! \{ans}\n")
end func