input: from typing import List
  
  
  def find_nth_fibonacci(n: int) -> int:
      """Finds the nth Fibonacci number.
      >>> find_nth_fibonacci(0)
      0
      >>> find_nth_fibonacci(1)
      1
      >>> find_nth_fibonacci(7)
      13
      >>> find_nth_fibonacci(-1)
      "Incorrect input"
      """
      if n < 0:
          return "Incorrect input"
      elif n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          return find_nth_fibonacci(n - 1) + find_nth_fibonacci(n - 2)
output:     
      if n < 0:
          return "Incorrect input"
      elif n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          a, b = 0, 1
          for _ in range(2, n + 1):
              a, b = b, a + b
          return b
  