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
