#!/bin/python3 import sys def sumOfGroup(k): # Return the sum of the elements of the k'th group. n = (k * (k+1)) - 1 k_sum = 0 while k: k_sum += n n -= 2 k -= 1 return k_sum if __name__ == "__main__": k = int(input().strip()) answer = sumOfGroup(k) print(answer)