#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    prevsum=0
    c=0
    for i in range(k):
        prevsum+=i
    start=2*prevsum+1
    #print(start)
    end=2*(prevsum+k)-1
    #print(end)
    for i in range(start,end+2,2):
        #print (i)
        c+=i
    return c

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