#!/bin/python3

import sys

def sumOfGroup(k):
    start = ((k-1)*k)//2
    end = (k*(k+1))//2
    
    total = 0
    for i in range(start, end):
        total += i*2 + 1
        
    return total
        
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)