The Johnsons have a second home that was available to rent for four full weeks $(28$ days$)$ during the summer. Of the twenty$-$eight days, the Johnsons rented it to unrelated tenants for $16$ days at fair market value. In addition, the Johnsons rented the home to the Florians for four days. Because they are family friends, the Florians only paid half the market rate for the rent. The Johnsons also rented the home for five days to the Smiths. The Smiths paid full fair market value rent even though they are related to the Johnsons. How many days did the Johnsons use the home for rental purposes during the year?