Obtaining values from the First Date and Last Date of a Table

I have the following table with Date and Cumulative Total. I need two measures - one is the cumulative total at the first day of a month (The first day might not start from 1st  always. The first date has to the the first date of this date set for that month). The second measure is the cumulative total at the last day of a month ( again, the last day has to be the last date of this date set for that month).