There are some pieces of candy on a table.You are challenged by your friend to play the  following game: you both have to altemate moves, and in each move, you can take away either $$1$$, $$2$$, $$3$$,~ $$4$$ or $$5$$ pieces from the table. The person who takes away the final piece 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->Combinatorics->Strategies and Operations->Game Strategy
Only $$18$$ is one of the multiples of $$5+1$$, and the second player can ensure victory. 