#!/bin/python3

import sys

def sumOfGroup(k):
    j=0
    for i in range(0,k):
        j=j+i
    K = 1 + (j-1) * 2 
    W = 0
    for x in range (0,k):
        K = K + 2
        W = W + K
    return W
        
    
    # Return the sum of the elements of the k'th group.

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