#!/bin/python3

import sys

def sumOfGroup(k):
    n = int(k)-1
    low = ((n*(n+1))//2)
    n = (low*2)+1
    sum=0
    for i in range(k):
        sum+= n
        n+=2
    return sum
        
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)