VN-TST 2016 Problem 2

Let $A$ be a set contains $2000$ distinct integers and $B$ be a set contains $2016$ distinct integers. $K$ is the numbers of pairs $(m,n)$ satisfying $$\begin{cases} m\in A, n\in B |m-n|\leq 1000 \end{cases}$$ Find the maximum value of $K$