def ask(x, y):
    print(f"? {x} {y}", flush=True)
    return int(input())


n = int(input())
for i in range(1, n, 2):
    res = ask(i - 1, i)
    if res == i - 1 or res == i:
        print(2 * i - 1 - res)
        exit()

print(n - 1)