#!/bin/python3

import sys
def sumOfGroup(k):
    s=0
    if k==1:
        return 1
    else:
        M = k * (k-1)
        N = k * (k+1)
        for i in range(M+1,N,2):
            s+=i
        return s
    

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