After two cycles, we have four copies. After three cycles, we're going to have eight copies. And the general equation that describes how many copies of DNA we can theoretically produce after N number of cycles is two to the power of N. So this gives us the number of copies of DNA after N number of cycles. And we can see after 20 cycles, we're going to have over 1 million copies. After 30 cycles, we're going to have over 1 billion of these copies. And we begin with a single DNA molecule whose DNA sequence we did not actually know.