Problems
Rooks on a chessboard
Rooks on a chessboard
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.
Examples
Input example #1
2
Output example #1
2