Dominoes are gaming pieces used in numerous tile games. Each domino piece contains two marks. Each mark consists of a number of spots (possibly zero). The number of spots depends on the set size. Each mark in a size ~N~ domino set can contain between 0 and ~N~ spots, inclusive. Two tiles are considered identical if their marks have the same number of spots, irregardless of reading order. For example tile with 2 and 8 spot marks is identical to the tile having 8 and 2 spot marks. A proper domino set contains no duplicate tiles. A complete set of size ~N~ contains all possible tiles with ~N~ or less spots and no duplicate tiles. For example, the complete set of size 2 contains 6 tiles:
Write a program that will determine the total number of spots on all tiles of a complete size ~N~ set.
The first and only line of input contains a single integer, ~N~ ~(1 \le N \le 1000)~, the size of the complete set.
The first and only line of output should contain a single integer, total number of spots in a complete size ~N~ set.
Sample Input 1
Sample Output 1
Sample Input 2
Sample Output 2
Explanation for Sample Output 2
Size 3 set contains tiles:
[0|0], [0|1], [0|2], [0|3], [1|1], [1|2], [1|3], [2|2], [2|3] and [3|3].
Sample Input 3
Sample Output 3