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