import math
def perm(a, b):
    return math.factorial(a + b) / (math.factorial(a) * math.factorial(b))

x = input()
N = int(x)
combi = 0

if N % 2 == 0:
    for n in range(int(N / 2) + 1):
        combi = combi + perm((2 * n), int((N - (2 * n)) / 2))
else:
    for n in range(int((N + 1) / 2)):
        combi = combi + perm(((2 * n) + 1), int((N - (2 * n)) / 2))
        
print(int(combi))