input: Write a function to calculate the Fibonacci sequence up to the nth term. The function should return the nth Fibonacci number. If the input is less than 0, the function should print "Incorrect input". Otherwise, it should compute the Fibonacci number and return it.
  def fibonacci(n): 
      a = 0
      b = 1
      if n < 0: 
          print("Incorrect input") 
      elif n == 0: 
          return a 
      elif n == 1: 
          return b 
      else: 
          for i in range(2,n): 
              c = a + b 
              a = b 
              b = c 
          return b 
  
  assert fibonacci(9)==34
  assert fibonacci(0)==0
  assert fibonacci(1)==1
  assert fibonacci(5)==5
  assert fibonacci(-1) is None
output: def fibonacci(n): 
      a = 0
      b = 1
      if n < 0: 
          print("Incorrect input") 
      elif n == 0: 
          return a 
      elif n == 1: 
          return b 
      else: 
          for i in range(2, n+1): 
              c = a + b 
              a = b 
              b = c 
          return b