#!/bin/python3

import sys

def sumOfGroup(k):
    n = 1
    suma = 0
    limit = 1
    if k==1:
        return 1
    while(k>1):
        if(k==2):
            for i in range(limit+1):
                n += 1
                suma += (2*n)-1
            break
             
        else:
            for i in range(limit+1):
                n += 1
        limit += 1
        k -= 1
    return suma 
        

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