A sequence of integers $$a_{1},a_{2},…$$ is chosen so that $$a_{n}=a_{n-1}-a_{n-2}$$ for each $$n\geq 3$$. What is the sum of first 2001 terms of the sequence if the sum of the first 1492 terms is 1985 and the sum of the first 1985 terms is 1492.

(第三届AIME1985 第5题)