one id code used in different tables

hi everybody

I have three tables, one of them is dimensional (id and names of my employees) and it has unique values. The others are fact tables, with diffenrent values (hours in differents sections or activities). I want to calculate total number of employees and I had some duplicated value because some people work in more than one activity. So, the measure shows more employees that I really have. Any idea about how to calculate this properly?

Thank you in advance.