lower = 0
upper = 10**9 + 1

while lower + 1 < upper:
    mid = (lower + upper) // 2
    print('? {}'.format(mid))
    ans = int(input())
    if ans == 0:
        print('! {}'.format(max(0, mid - 1)))
        break
    if ans == 1:
        lower = mid
        upper -= 1
    if ans == -1:
        upper = mid - 1
        lower = max(0, lower - 1)
else:
    print('! {}'.format(lower))