Sum of forces in a group

Hello everybody,

I want to write out the sums of the forces in x, y, and z of all particles in a defined group at eveyr 100 steps.
So I create a region

region count1 block -0.7 0.7 -3.0 -1.5 0.0 0.6 units box

then I create a goup

group count1 region count 1

But how to go on. I read in the manual about the compute property/atom command. As I understand this command will calculate e.g. the forces in x,y and z per atomand per step. But how to handle this. Is this the right way to solve my problem. How can I make these forces readable for me, maybe as an export?

I hope you can help me. Thanks a lot and
best regards,
Nils