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 domino set can contain between 0 and 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 contains all possible tiles with 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 set.

#### Input Specification

The first and only line of input contains a single integer, , the size of the complete set.

#### Output Specification

The first and only line of output should contain a single integer, total number of spots in a complete size set.

#### Sample Input 1

`2`

#### Sample Output 1

`12`

#### Sample Input 2

`3`

#### Sample Output 2

`30`

#### 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

`15`

#### Sample Output 3

`2040`

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