import sys

LIMIT = 10**6

prev = LIMIT + 1
print("?", prev)

ok, ng = 1, LIMIT + 1

while abs(ok - ng) > 1:
    mid = (ok + ng) // 2
    curr = 2 * mid - prev - 1

    print("?", curr)

    if (int(input()) == 1) == (prev < curr):
        ok = mid
    else:
        ng = mid

    prev = curr
    print("ok, ng:", ok, ng, file=sys.stderr)

print("!", ok)