I got a YES for the first submission.
I learned that devising and testing program on a paper is quite effective. It's easier to edit and modify. Once you've finished coding, it's harder to modify your program.
And devising at least several test cases before submitting your program. It's quite often that the Sample is somewhat misleading, there used to be long way between YES and merely making your program pass the Sample test.

Most importantly, I can feel some improvement on my coding skills no matter how easy the problem I'm trying to solve seems to be. Just write your code, once day you will feel the improvements.