#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    a = (k*(k-1))+1;
    temp = long((k*((2*a)+(k-1)*2))/2);
    return temp;

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