input: Write a function to generate Fibonacci numbers recursively in Python. The function should take an integer `n` as input and return the nth Fibonacci number. If `n` is 1 or 2, the function should return 1. Otherwise, the function should return the sum of the (n-1)th and (n-2)th Fibonacci numbers. If `n` is less than 1, the function should return 0.
  
  assert fibonacci(1)==1
  assert fibonacci(2)==1
  assert fibonacci(10)==55
  assert fibonacci(20)==6765
  assert fibonacci(0)==0
  assert fibonacci(-1)==0
output: def fibonacci(n):
      if n < 1:
          return 0
      elif n == 1 or n == 2:
          return 1
      else:
          return fibonacci(n-1) + fibonacci(n-2)