headcount visual for new joiners

Hi Guys, I'm creating a headcount visual for new joiners. the source data that I get comes in a form of Year to date rather then Period to Date. so when I write my measure to count all the new joiners I get the following numbers, March 39, April 61, Total 100. what I want to get is 39 in march and 22 in April. = April number minus March Number, going forward it would be May number minus March number etc. is there a way to do this ?

my table looks like so: team name // FTE Alpha 5 Bravo 3 Charlie 4 Delta 5 Echo 1 Foxtrot 6 Golf 9 Hotel 17 India 4 how can I write a measure so that it sums up all the FTE's except for FTE's in teams India & Foxtrot ?