input: Write a function to calculate the nth Fibonacci number recursively.
  assert Fibonacci(1)==0
  assert Fibonacci(2)==1
  assert Fibonacci(5)==3
  assert Fibonacci(10)==34
output: def Fibonacci(n):
      if n == 1:
          return 0
      elif n == 2:
          return 1
      else:
          return Fibonacci(n-1) + Fibonacci(n-2)