#!/bin/python

import sys

def sumOfGroup(k):
    sumofnum=0
    numelements = 0
    j=k
    while j > 0:
       numelements = numelements + (j-1)
       j = j -1 
    endelements = numelements+k
    for i in xrange(numelements,endelements):
        sumofnum = sumofnum + (2*i + 1)
    return sumofnum
    # Return the sum of the elements of the k'th group.

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