n = int(input())
for i in range(0, n - 1, 2):
    print('?', i, i + 1)
    x = int(input())
    if i == x:
        print('!', i + 1)
        break
    elif i + 1 == x:
        print('!', i)
        break
else:
    print('!', n - 1)