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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
__author__ = 'MARI'


def main():
    a = int(input())
    print(1 + 12*(a*(a-1)//2))


if __name__ == '__main__':
    import sys

    argv = sys.argv
    main()
