#!/bin/python3

import sys

def sumOfGroup(k):
    n = (((k-1) * k) // 2) + 1
    a = (2*n) - 1
    l = (2*(n+k-1)) - 1
    return (k*(a+l)) // 2

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