39. Aladdin used the magic lamp to summon the genie, who said to Aladdin: “You can choose some numbers from the natural numbers 1, 2, 3, 4, 5, $\qquad$ 2019, 2020 such that the sum of any two numbers is not an integer multiple of their difference. The number of numbers you choose, I will give you that many gold coins.” Therefore, the maximum number of gold coins Aladdin can get is $\qquad$.
$674$