def jiMu(n):
        #1,3,6,10,15
        s = 0
        if n == 1:
                s = 1
        else:
               s = jiMu(n-1) + n 
        return s
n = int(input())
s = 0
for i in range (1,n +1):
        s += jiMu(i)
print(s)

/**************************************************************
	Problem: 1148
	User: admin
	Language: Python
	Result: Accepted
	Time:144 ms
	Memory:34480 kb
****************************************************************/