n = int(input())

x, y = 0, 1
for _ in range(n // 2):
    print(f"? {x} {y}")
    z = int(input())
    if z == x:
        print(f"! {y}")
        exit()
    if z == y:
        print(f"! {x}")
        exit()
    x = (x + 2) % n
    y = (y + 2) % n
print("! " + str(n - 1))