n = int(input())

i = 0
ans = 0

def AAA(a , b):
	a1,b1 = 1,1
	for i in range(b):
		a1 *= a - i
	for i in range(b):
		b1 *= b - i
	return a1 // b1
	

while True:
	if 2 * i > n:
		break
	ans += AAA((n - i) , i)
	i += 1

print(ans)