n = int(input())
now = 0
while True:
	print(f"? {now} {now + 1}")
	x = int(input())
	if x == now:
		print(f"! {now + 1}")
		exit()
	if x == now + 1:
		print(f"! {now}")
		exit()
	if now == n-1:
		print(f"! {n-1}")
		exit()
	now += 2