input: Write a function to generate the nth Fibonacci number using a recursive approach in Python. If n is 1 or 2, return 1. Otherwise, return the sum of the two preceding Fibonacci numbers. If n is less than 1, return 0.
  assert fibonacci(10)==55
  assert fibonacci(1)==1
  assert fibonacci(2)==1
  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)