ans_min = 0
ans_max = 10**9
while True:
    print("? ",(ans_min+ans_max)//2)
    ans_ans = int(input())
    if ans_ans == 1:
        ans_min = ans_ans
    else:
        ans_max = ans_ans
    if ans_max - ans_max == 1:
        print(ans_min)
        exit()