input: Write a function to generate a Fibonacci sequence of the first n numbers. If n is 1, return 0. If n is 2, return 1. For any other value of n, return the sum of the previous two Fibonacci numbers.
  
  assert Fibonacci(5)==3
  assert Fibonacci(10)==34
  assert Fibonacci(1)==0
  assert Fibonacci(2)==1
  assert Fibonacci(7)==8
output: def Fibonacci(n):
      if n == 1:
          return 0
      elif n == 2:
          return 1
      else:
          a, b = 0, 1
          for _ in range(3, n + 1):
              a, b = b, a + b
          return b