input: 
  
  def fib4(n: int):
      """The Fib4 number sequence is a sequence similar to the Fibbonacci sequnece that's defined as follows:
      fib4(0) -> 0
      fib4(1) -> 0
      fib4(2) -> 2
      fib4(3) -> 0
      fib4(n) -> fib4(n-1) + fib4(n-2) + fib4(n-3) + fib4(n-4).
      Please write a function to efficiently compute the n-th element of the fib4 number sequence.  Do not use recursion.
      >>> fib4(5)
      4
      >>> fib4(6)
      8
      >>> fib4(7)
      14
      """
  
output:     if n == 0:
          return 0
      elif n == 1:
          return 0
      elif n == 2:
          return 2
      elif n == 3:
          return 0
      
      a, b, c, d = 0, 0, 2, 0
      for _ in range(4, n + 1):
          a, b, c, d = b, c, d, a + b + c + d
      
      return d