There are some pieces of candy on a table. You are challenged by your friend to play the following game: The two players take turns taking some candy. Every turn, you can take away either $$1$$, $$2$$, $$3$$, $$4$$ or $$5$$ pieces from the table. The person who takes away the final piece of candy from the table wins. If you go second, how many pieces of candy should be on the table before the game starts such that you can ensure victory? 
Overseas Competition->Knowledge Point->Counting Modules->Permutations and Combinations->Combinations
Only $$18$$ is one of the multiples of $$5+1$$, and the second player can ensure victory. 