x= int(input())
def function_A(x):
    A = [0]*(x+1)
    if x >= 1:
        A[1] = 0
    if x >= 2:
        A[2] = 1
    if x >= 3:
        A[3] = 1
    for i in range(4,x+1):
        A[i] = A[i-3]+2*A[i-2]+A[i-1] 
    return A
A = function_A(x)
print(A[x])