#!/bin/python3

import sys

def sumOfGroup(k):
    start =1;
    if (k ==1):
        return 1
    i = 0
    for i in range (2,k+1):
        start  = start + 2* (i-1);    
    
    
    sum1 =0;
    it_value =0;
    for j in range(0,k):
        it_value = start + 2 * j;       
        sum1 = sum1 + it_value;
    
    return sum1;

    

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