#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    ans = 0
    if k == 1:
        return(1)
    else :
        prev = (k * (k-1))//2
        for i in range(k):
            ans += 2*prev + 1
            prev += 1
        return(ans)

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