import sys
import math

ans = 0
low = 1
high = 1e9 + 1
mid = (low + high) // 2 + 1
beforemid = 0

while True :
	mid = (low + high) // 2
	print("?", mid)
	sys.stdout.flush()
	res = int(input())

	if res == 1 :
		low = mid
	else :
		high = mid

	if math.fabs(beforemid - mid) == 0 :
		break

	beforemid = mid

if res == 0 :
	mid = mid - 1

print("!", mid)
sys.stdout.flush()