#!/bin/python import sys def oddnum(p): count=1 n=1 while count<=p: n+=2 count+=1 return n def sumOfGroup(k): i=1 j=1 while i<k: # Return the sum of the elements of the k'th group. j+=i i+=1 grpstr=oddnum(k) sumgrp=0 for m in range(0,k): sumgrp+=grpstr grpstr+=2 return sumgrp if __name__ == "__main__": k = int(raw_input().strip()) answer = sumOfGroup(k) print answer