Running Total issue

Hi everyone,

I have sales and Calendar tables which have following columns :

Sales :

-Id

-OrderDate

-DeliveryDate

-Amount

Calendar table (Marked as Date table)

-Date

There is a relationship between Sales(OrderDate) and Date(Date)

I create a measure RunningTotal = 

IF(MIN(Calendar [Date]) <= CALCULATE(MAX(Sales(OrderDate);ALL(Sales))

;CALCULATE(SUM(Sales[Amount]);FILTER(ALL(Calendar );Date[Date]<= MAX(Calendar [Date]))))

 

My problems is when i have no amount in sales table "runningtotal" is blank instead of having the value of the previous month

 

eg: for august 18 i want to display 79700,84

how can i achieve this?

 

Here my data

 

Thank you in advance