\includegraphics{https://static.e-olymp.com/content/cc/cc5ac35eb2f57ca4817959d1eec9a2aa0d5ca34b.jpg} From the childhood little Garik was interested in a question: in how many ways $n$ rooks can be arranged on the chessboard of size $n \times n$ so that they do not hit each other. He was solving this puzzle for a long time for each case, and when he solved the problem --- he gave up the chess. And how fast can you solve this puzzle? \InputFile The size of the chessboard $n~(n \le 1000)$. \OutputFile Print the answer, found by Garik.