M+M-1M+M-2M+M-3M+M-4M+M-5M+M-6M+M-7M+M-8M+M-9M+M-10M+M-11M+M-12M+M-13M+M-14M+M-15M+M-16M+M-17M+M-18M+M-19M+M-20