On a report, how to relate tasks date with contact?

Hi all,

I have a doubt here that I cannot find the answer to online.

I am creating a report which has to show all contacts within certain groups (so far so good) but that had nothing happening for more than 1 month.

So for that, I have to check if no task within the last month is associated with each contact, but I see no ID field from contact to relate to, on the tasks. I only see the full name and that cannot be comparable because there are people with same names.

Can someone give me a hand on solving this?

Thank you very much in advance.

Best regards,
Pedro Lima