#!/bin/python

import sys

def sumOfGroup(k):
    ans = 0;
    if (k%2 != 0):
        start = k*(k-1)+1;
        beg = start
        for x in range(k-1):
            beg = beg + 2;
            start += beg;
    else:
        start = k*(k-1)+1;
        beg = start;
        for x in range(k-1):
            beg = beg+2
            start += beg
    return start;   

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