input: 
  def distance_between_points(x1: int, y1: int, x2: int, y2: int) -> float:
      """Calculate the Euclidean distance between two points on a two-dimensional plane.
      >>> distance_between_points(3, 4, -9, -2)
      13.416407864998739
      """
  
output:     return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5