n = int(input())
def f(n):
    if n == 1:
        return 0
    elif n == 2 or n == 3:
        return 1
    else:
        return f(n-3) +2*f(n-2)+f(n-1)
print(f(n))

n = 4

return f(1) +2*f(2) +f(3)

return 0 +2 + 1

reutrn 3