#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    
    if k == 1:
        return 1
    
    num = k * (k - 1) + 1
    sum = num
    
    for i in xrange(k - 1):
        num += 2
        sum += num
        
    return sum
    

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