#!/bin/python3

import sys

def sumOfGroup(k):
    b=int((k*(k-1))/2)
    q=(2*b)+1
    i=0
    answer=q*k
    w=0
    while i<k:
        answer=answer+w
        w=w+2
        i=i+1
    return int(answer)
    # Return the sum of the elements of the k'th group.

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