Need to Calculcate Networkdays using Calcucated Measures in Power Pivot

Question

I Need to Calculate Network days using power pivot calculated fields.
My First Problem is Every column has Blank values.
Second Issue is that, I have to calculate the network days using three different date columns.
IF the first and second column has the non blank cells then I don't have to move forward. but if the second column have any blank values, then it has to move to third column and should find the network days between first and third column.

Please find the attached screenshot for details information. I am able to do it by creating some manipulated columns in the spreadsheet. However I would like to know, if we can create the same using the DAX expressions in Calculated fields.