input: Write a function to generate Fibonacci numbers up to a given number. If the given number is zero, return zero. If the given number is one, return one. Otherwise, return the sum of the two previous numbers in the sequence.
  def Fibonacci(n): 
  	if n==0: 
  		return 0
  	if n==1: 
  		return 1
  	else: 
  		return Fibonacci(n-1)+Fibonacci(n-2)
  assert Fibonacci(0)==0
  assert Fibonacci(1)==1
  assert Fibonacci(5)==5
  assert Fibonacci(10)==55
output: def Fibonacci(n): 
      if n == 0: 
          return 0
      elif n == 1: 
          return 1
      else: 
          a, b = 0, 1
          for _ in range(2, n + 1):
              a, b = b, a + b
          return b