Total amount in Campaigns

Hi,

How can I have a field in Campaigns that sums the total amount of potentials that are in relation with that campaign?

Now i get the total amount of all potentials linked to a campaign by a report, and i want the sum in Campaigns module

I tried to create a formula field on Campaigns that make the sum of amounts displayed in the potentials, and it didn't work, maybe because its inormation that is in the potentials form (module).

Is it possible to create this field?

How can I create this suma field?

Regards.