Avg calculation macro

Hi Guru's

Can you help me developing avg calculation macro with the below logic.

Key figure

M0 (current)

M1

M2

M3

M4

M5

Forecast

0

0

26

30

0

62

Average of requested plan: Number of months considered: from M2 to M5, total 4 months; Total requested plan: 26 + 30 + 62= 118

Average Requested plan: = 118/4 = 30

Thanks,

Rajeev