6. (10%) Simplify the following compound proposition to minimize the number of "and", "or", and "not" operations. $$(p \wedge q \wedge r) \vee (\neg p \wedge \neg r \wedge \neg s) \vee (\neg p \wedge \neg q \wedge s) \vee (\neg p \wedge q \wedge s) \vee (\neg p \wedge r \wedge \neg s)$$