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