import math

n = int(input())

l = [[i, j] for i in range(n) for j in range(n) if i + 2*j == n]

def c(n, r):
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))

x = 0
for i, j in l:
    x += c((i+j), i)

print(x + 1)