A store tracks the number of headphones it has in stock and how many it sells. At the beginning of the week the store had 26 pairs. On Monday the inventory changed by -3, on Tuesday the inventory changed by -1, on Wednesday the inventory changed by 15 pairs in the morning and -6 in the afternoon, on Thursday the inventory changed by -3, and on Friday the inventory changed by -2 but also had +1. When the store opened on Saturday morning, how many pairs did it have in inventory?