Byte and Chess

While rushing to class, Baytik noticed a chessboard in the game room. He began to wonder how many different squares of side length k (1 ≤ k ≤ n) can fit on a chessboard of size n.

Input

A natural number n (n ≤ 10000), representing the size of the chessboard.

Output

A single number indicating the total number of different squares that can be placed on the chessboard.

Examples