Summing Differences in Login/Logout Times

I have created a measure that sums the number of days (counting calendar dates, not full 24 hour days) by using the following:

Days Duration = SUMX ( 
        Sheet1,
        DATEDIFF ( Sheet1[Login], Sheet1[Logout], Day )
    ) +1

Based on this data below, I would like to see the sum total of these days. So instead of gettting a "5" I would expect to see a "9".

Thank you