You can buy thirty or forty pieces, but in a few days, the bottom of the pot will be uneven and the oil smoke will be bigger. Anyway, you can use it, but if you want to use it conveniently and cheaply, you'd better go to the market and buy the kind of seventy or eighty. It's best to buy a thicker material, which doesn't stick to the pan, has less oil smoke and is not easy to paste. If you go to the supermarket, you won't feel so good about seventy or eighty.