prev = 10**6 + 1
print("?", prev)

ok, ng = 1, 10**6
while abs(ok - ng) > 1:
    mid = (ok + ng) // 2
    curr = 2 * mid - prev
    
    print("?", curr)
    
    if (int(input()) == 1) == (prev < curr):
        ok = mid
    else:
        ng = mid
    prev = curr

print(ok)