What is the expiation for someone who swore by Allah Almighty in writing to do something for a specific period, but then did not complete the agreed-upon period?

Whoever swears by Allah to do something is obligated to do it; otherwise, an expiation for breaking an oath (kaffarat yamin) becomes due. The expiation for breaking an oath is: feeding ten needy people, or clothing them, or freeing a slave. If one cannot find these, then fasting for three days, as Allah the Almighty says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever does not find [the means] - then a fast of three days. That is the expiation for oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful." (Al-Ma'idah: 89).