def fib(n):
  """This function returns the nth Fibonacci numbers."""
  i = 0 # variable i = the first fibonacci number
  j = 1 # variable j = the second fibonacci number
  n = n - 1 # variable n = n - 1

  while n >= 0: # while n is greater than 0
    i, j = j, i + j # 0, 1 = 1, 0 + 1
    n = n - 1 # we want the script to add the number preceeding it
  
  return i