I need to add a custom date to a lead that calculates the last time a sales rep personally contacted the lead.

Problem is, my marketing automation system (Autopilot) is adding a lot of activity records so I Last Activity Date does not work.

Fortunately, Autopilot prefixes all activity subjects with "[Autopilot]". 

Is there a way to create a custom field that calculates the date of the most recent activity, where the subject does not contain "[Autopilot]"?

Thanks in advance