Below we will define an n-interesting polygon. Your task is to find the area of a polygon for a given n.

A 1-interesting polygon is just a square with a side of length 1. An n-interesting polygon is obtained by taking the n - 1-interesting polygon and appending 1-interesting polygons to its rim, side by side. You can see the 1-, 2-, 3- and 4-interesting polygons in the picture below.

Example

• For n = 2, the output should be**solution(n) = 5**;
• For n = 3, the output should be**solution(n) = 13**.

Input/Output

• [execution time limit] 3 seconds (java)

• [memory limit] 1 GB

• [input] integer n

  Guaranteed constraints:

  1 ≤ n < 104.

• [output] integer

  The area of the n-interesting polygon.

풀이

• 그림을 보면 n 이 증가할 때의 사각형 개수는 n^2 개의 사각형과 (n - 1)^2 의 사각형의 합을 이룬다.

int solution(int n) {
    return (n * n) + ((n - 1) * (n - 1));
}