Hi Subrahmanyam,
Vadim is asking whether you have any parent available for Mem1 & Mem2 in account dimension so that you will get the sum automatically rolling up in the parent.
Please check the feasibility of creating a new parent for Mem1 & Mem2 in the account dimension.
else the last option would be creating a local member in the report having Time and Account in column axis and create a local member using " insert after" and "Dimension" (Account).
In the formatting sheet apply formula for local member by using content override option.
Thanks,
Dinesh.V