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Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
# -*- coding: utf-8 -*-
import sys

if __name__ == '__main__':

    num = map(int,sys.stdin.readline().split())
    n = num[0]

    print 6 * n ** 2 - 6 * n + 1