import sys
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)
        
for line in sys.stdin:
    a = line.split()
    a=int(a[0])
    print(f(a))
        # print(int(a[0]) + int(a[1]))