N = int(input())
for i in range(N//2):
    print('?',i*2,i*2+1)
    z = int(input())
    if z==i*2:
        print('!',i*2+1,flush=True)
        exit()
    if z==i*2+1:
        print('!',i*2,flush=True)
        exit()
print('!',N-1,flush=True)