input: Write a function to compute the nth Fibonacci number using a recursive approach. The input parameter n should be an integer, and the function should return an integer representing the nth Fibonacci number. If n is 0, the function should return 0. If n is 1, the function should return 1. For any other value of n, the function should return the sum of the (n-1)th and (n-2)th Fibonacci numbers.
  
  assert fibonacci(0)==0
  assert fibonacci(1)==1
  assert fibonacci(6)==8
  assert fibonacci(10)==55
  assert fibonacci(15)==610
output: def fibonacci(n):
      if n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          return fibonacci(n-1) + fibonacci(n-2)