#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    s=k*(k-1)/2
    tn=1+((s+1)-1)*2
    final=0
    for a in range(0,k):
        final+=tn
        tn+=2#chk
    return final

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