Is it obligatory to fast the three days as expiation for an oath, in addition to fasting the thirty days that were vowed?

If someone swears to abandon a sin, and then swears that he will fast for thirty days if he commits it, then if he breaks his oath and commits the sin, he owes two expiations (kaffarat): the first for breaking his oath regarding abandoning the sin, and the second for not fasting the thirty days. However, if he fasts the thirty days after committing the sin, then he only owes one expiation. The expiation for an oath is feeding ten needy persons, or clothing them, or emancipating a slave. If he is unable to do so, then he must fast for three days. Abandoning sin is inherently obligatory, and swearing an oath to abandon it merely emphasizes this obligation.