def shulie(n):
    if n<1:
        return False
    if n==1:
        return 0
    if n==2 or n==3:
        return 1
    if n>=4:
        a=n-3
        b=n-2
        c=n-1
    return shulie(a)+2*shulie(b)+shulie(c)
n=int(input())
print(shulie(n))