Report to find opportunities where 1 particular activity has not been created

Hi Team, 

Is it possible to find the opportunities that do not have a specific activity?

I need to find the opportunities without a specific activity: this means that I need to find the opts without activities + those without this specific activity. 

With Cross Filter, I select one or the others but I don't find a way to select both.

Do you have an idea?

Thanks!

#Reports & Dashboards