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

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

#### Output

Print the answer, found by Garik.

Input example #1

2

Output example #1

2