I have a 15ft x 36in (4.57m x 91 cm) pool and the mats i wanna buy are 20.5-in x 20.5-in. How many mats would i need to put under the pool?

I have a 15ft x 36in 457m x 91 cm pool and the mats i wanna buy are 205in x 205in How many mats would i need to put under the pool class=