min_x = 0
max_x = 10**9
correct = false
while !correct
	x = (max_x - min_x) / 2 + min_x
	print "? #{x}\n"
	STDOUT.flush
	y = gets.strip.split(' ')[1].to_i
	if x == y
		break
	elsif y == 1
		max_x = (max_x - min_x) / 2 + min_x
	else
		min_x = (max_x - min_x) / 2 + min_x
	end
end