What is the expiation for intercourse with one's wife during Ramadan before Iftar unintentionally?

The expiation for intentional intercourse during the daytime in Ramadan, while being mindful and fasting, is to free a slave. If one is unable to do so, then it is to fast for two consecutive months. If one is unable to do that, then it is to feed sixty poor people. As for intercourse due to forgetfulness of the fast, there is no expiation for it, but one must make up that day, in accordance with the hadith: "Mistake and forgetfulness have been lifted from my nation."