Problems

# Rooks on a chessboard

# Rooks on a chessboard

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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.

Input example #1

2

Output example #1

2