Count the Regions

Time Limit: 2 Seconds
Memory Limit: 65536 KB

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

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*

Author:

**SHEN, Guanghao**
Source:

**ZOJ Monthly, October 2003**
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