def sort_by_dnf(arr, n):
  
  low=0
  mid=0
  high=n-1
  while mid <= high:
    if arr[mid] == 0:
      arr[low], arr[mid] = arr[mid], arr[low]
      low = low + 1
      mid = mid + 1
    elif arr[mid] == 1:
      mid = mid + 1
    else:
      arr[mid], arr[high] = arr[high], arr[mid]
      high = high - 1
  return arr
def count_ways(n):
	 
	A = [0] * (n + 1) 
	B = [0] * (n + 1) 
	A[0] = 1
	A[1] = 0
	B[0] = 0
	B[1] = 1
	for i in range(2, n+1): 
		A[i] = A[i - 2] + 2 * B[i - 1] 
		B[i] = A[i - 1] + B[i - 2] 
	return A[n] 