What is the expiation for multiple oaths, many of which have been forgotten?

If a person swears multiple oaths concerning a single act, and then breaks all of them, only one expiation is required of him. However, if he swears multiple oaths concerning different acts, and then breaks all of them, he is required to offer expiations equal to the number of acts he broke his oath for. And if he is ignorant of the number of oaths, he must offer expiation for what he believes will clear his conscience.