input: Write a python function to calculate the distance between two points (x1, y1) and (x2, y2).
  assert calculate_distance(2, 3, 6, 8) == 6.4031242374328485
  assert calculate_distance(1, 1, 4, 5) == 5.0
  assert calculate_distance(0, 0, 0, 0) == 0.0
output: def calculate_distance(x1, y1, x2, y2):
      return ((x2 - x1)**2 + (y2 - y1)**2)**0.5