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ZOJ Problem Set - 1629
Counting Triangles

Time Limit: 2 Seconds      Memory Limit: 65536 KB

Given an equilateral triangle with n the length of its side, program to count how many triangles in it.


Input

The length n (n <= 500) of the equilateral triangle's side, one per line.

process to the end of the file


Output

The number of triangles in the equilateral triangle, one per line.


Sample Input

1
2
3


Sample Output

1
5
13



Author: JIANG, Jiefeng
Source: ZOJ Monthly, June 2003
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