input: Write a function to calculate the Fibonacci numbers up to a given number n. The function should return the nth Fibonacci number. If n is 0, it should return 0. If n is 1, it should return 1. For n greater than 1, it should return the sum of the two preceding Fibonacci numbers.
  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
  assert Fibonacci(15)==610
output: def Fibonacci(n): 
  	if n==0: 
  		return 0
  	if n==1: 
  		return 1
  	else: 
  		return Fibonacci(n-1)+Fibonacci(n-2)