#include <bits/stdc++.h>
int main() {
  int n, i, sum = 0;
  scanf("%d", &n);
  if (n == 1) sum = 1;
  if (n == 2) sum = 5;
  if (n == 3) sum = 13;
  if (n >= 4) {
    for (i = 4; i <= n; i++) {
      sum = sum + i * i - (i - 2) * (i - 2);
    }
    sum = sum + 13;
  }
  printf("%d", sum);
}

### Prompt

Your task is to create a CPP solution to the following problem:

While playing with geometric figures Alex has accidentally invented a concept of a n-th order rhombus in a cell grid.

A 1-st order rhombus is just a square 1 × 1 (i.e just a cell).

A n-th order rhombus for all n ≥ 2 one obtains from a n-1-th order rhombus adding all cells which have a common side with it to it (look at the picture to understand it better).

<image>

Alex asks you to compute the number of cells in a n-th order rhombus.

Input

The first and only input line contains integer n (1 ≤ n ≤ 100) — order of a rhombus whose numbers of cells should be computed.

Output

Print exactly one integer — the number of cells in a n-th order rhombus.

Examples

Input


1


Output


1

Input


2


Output


5

Input


3


Output


13

Note

Images of rhombus corresponding to the examples are given in the statement.

### Response

```cpp
#include <bits/stdc++.h>
int main() {
  int n, i, sum = 0;
  scanf("%d", &n);
  if (n == 1) sum = 1;
  if (n == 2) sum = 5;
  if (n == 3) sum = 13;
  if (n >= 4) {
    for (i = 4; i <= n; i++) {
      sum = sum + i * i - (i - 2) * (i - 2);
    }
    sum = sum + 13;
  }
  printf("%d", sum);
}

```