[LuLu49]

This will be a bit of a slog
M(1,1) = 1 so P(M=1) = 1/36
M(2,2) = 2 has prob of 1/36
M(1,2) = 2 has prob of 2 x 1/36 = 2/36
P(M=2) = 3/36
etc
CDF(M=1) = 1/36
CDF(M=<2) = 1/36 + 3/36 = 4/36
etc
Make sure that CDF(M=<6) = 1 and you should be OK