N = int(input())

import sys

now = 1
dat = [0] * (N + 1)
while True:
    for i in range(2,N // now + 1):
        if now * i > N:
            print("!",now)
            exit()
        if dat[now * i] == 1:continue
        print("?",now*i)
        s = int(input())
        if s == now * i:
            now = now * i
            break
        else:
            for j in range(now*i,N+1,now*i):
                dat[j] = 1