#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    T1 = (k*(k-1)/2+1)*2-1
    Sn = k*T1+k*(k-1)
    return Sn

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