#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    num = (k-1)*k+1
    result = 0
    for _ in range(k):
        result += num
        num += 2
    return result

if __name__ == "__main__":
    k = int(raw_input().strip())
    answer = sumOfGroup(k)
    print answer