Master Zhang made a batch of parts. On the first day, he made 20 parts. After that, he made 2 more parts every day than the previous day. On the 30th day, he made 78 parts, which was just finished. How many parts are there in this batch?
张师傅做一批零件，第一天做了20个，以后每天都比前一天多做2个，第30天做了78个，正好做完．这批零件共有几个？
<result>1_470</result>