Hey everyone and thanks for taking the time.

Here is some sample data, that I will use to explain my problem with.
Covid Cases March April May June
Germany 67 98 30 78
Sweden 12 45 40 35





I am looking for a way to get the cumulative number of cases for a specific month. The end result should look like this:
Covid Cases March April May June
Germany 67 165 195 273
Sweden 12 57 97 132
How would I do this?

This is probably very easy, but I couldn't find an explanation so far.

Thanks for taking the time.