Need a formula for 2 columns with a list of start and end dates and excel will give the total without double counting overlapping dates

To give more context, I'm tracking project timelines and unfortunately I'm just a bean counter. Structurally we would ideally have everyone record when they start and stop, but at my level best I can do is add up all the roadblocked time then subtract it from the total.

So if I put all my start times in Col A and end times in Col B and just have excel do all the math and wash out the dates that overlap - what would my formula be?