"Choose the proper Multiplexer for solving the equation: F=Σ(1,3,5,7,9,11). Give the table of truth of the multiplexer, as well as a drawing of the circuit."

I guess a 4bit MUX and consecutively selecting each of the 6 numbers above in their binary form to let the MUX give them as an output does the trick, but what then? How to I get the "Σ" of them? Should I use a circuit to store the numbers, then add them? I'm a bit confused, because I remember in these past exams some people tried something with a simple gate, which I don't recall. Sorry If I sound like a noob Any help appreciated!