n = int(input())
total_sum = 0
for i in range(1, n + 1):
    factorial = 1
    for j in range(1, i + 1):
        factorial *= j
    total_sum += factorial
print(total_sum)
    
/**************************************************************
	Problem: 1019
	User: fuyijun
	Language: C++
	Result: Compile Error
****************************************************************/