Consider 3 parties, Alice, Bob and Charlie. Suppose each party has a bit as input, i.e. Alice, Bob and Charlie hold $a, b, c \in \{0, 1\}$ respectively. Show how construct a scheme with which they can compute the function $f (a, b, c) = a + b + c$ such that the following are satisfied:

(1) All parties learn $f(a, b, c)$ at the end.

(2) No party can learn more about the other party's input than what they can infer from $f(a, b, c)$ and choosing their own input wisely.