n =  int(input());
s = 0;
for i in range(1, n + 1):
    k = 1;
    for j in range(1,i+1):
        k  *= j;
    s = s + k;

print(s);

/**************************************************************
	Problem: 1019
	User: admin
	Language: Python
	Result: Accepted
	Time:87 ms
	Memory:34244 kb
****************************************************************/