#!/bin/python import sys def sumOfGroup(k): # Return the sum of the elements of the k'th group. a = range((k*(k-1)/2)+1,(k*(k-1)/2)+k+1) a = [2*i-1 for i in a] return sum(a) if __name__ == "__main__": k = int(raw_input().strip()) answer = sumOfGroup(k) print answer