Excel: Sum N rows, then skip M rows

I'm encountering a problem I can't seem to figure out. I have a large data set in Excel and need to (see figure):

1. sum n rows (red in figure)
2. skip m rows (black line in figure)
3. sum n rows again (blue in figure)
   etc etcThe pattern is repetitive

I have searched everywhere, but I'm only able to find answers regarding summing n rows, but not the skipping rows part.

Kind regards