Rooks on a chessboard

Rooks on a chessboard

Time limit 1 second
Memory limit 128 MiB

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 × 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?

Input data

The size of the chessboard - a positive integer not greater than 1000.

Output data

Print the answer, found by Garik.


Input example #1
Output example #1
Author Анатолий Присяжнюк