Counting equilateral triangles

Small equilateral triangles of side length 1 are stacked into a triangular tower of $N$ layers. Count how many equilateral triangles, large and small together, the lines of that figure form. Triangles pointing up and triangles pointing down both count, and every side length from 1 small triangle up to $N$ small triangles counts.

When $N$ is 2, the answer is 5.

The first line contains the layer count $N$ of the triangular tower. ($1 \le N \le 10{,}000$)

Print the total count of triangles, large and small together, on the first line.