Warren and Naida make a list of numbers. They start with 0, then Warren adds 20, thenNaida subtracts 1, then Warren adds 19, then Naida subtracts 2

Warren and Naida make a list of numbers. They start with 0, then Warren adds 20, then
Naida subtracts 1, then Warren adds 19, then Naida subtracts 2.
0, 20, 19, 38, 36, . . .
This pattern continues until Warren adds 1 and Naida subtracts 20, which ends up back
at 0. What is the largest number in their list?