Problem Description

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.

1
2
3

1
5
13

Author

JIANG, Jiefeng