def main():
    def ask(m):
        print("?", m)
        res = int(input())
        return res

    l, r = 0, 10 ** 9 + 1
    while l + 1 < r:
        m = (l + r) // 2
        if ask(m): l = m
        else: r = m
    print("!", l)

main()