Hexagonal numbers are figurate numbers which can be calculated using the formula hn = 2n2 - n. You are given n; calculate n-th hexagonal number.

Input

The only line of input contains an integer n (1 ≤ n ≤ 100).

Output

Output the n-th hexagonal number.

Examples

Input

3


Output

15


Input

6


Output

66

Source: codeforces | Difficulty: EASY


Solutions: