# Count the Regions

Time Limit: Java: 2000 ms / Others: 2000 ms

Memory Limit: Java: 65536 KB / Others: 65536 KB

## Description

What's the maximum number of regions definable by N zig-zag lines, each of which consists of two parallel infinite half-lines joined by a straight line segment?

Here is an example of 2 zig-zag lines yield 12 regions at the most.

## Input

The input consists of a sequence of N (<= 10000), which is the number of the zig-zag lines, one per line.

## Output

For each N, you should output the number of the maximum regions.

## Sample Input

1
2

## Sample Output

2
12

None

## Source

ZOJ Monthly, October 2003