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ZOJ Problem Set - 1652
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



Author: SHEN, Guanghao
Source: ZOJ Monthly, October 2003
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