input: Write a function to calculate the distance between two points on a two-dimensional plane. The function should take four inputs, representing the x and y coordinates of two points, and return the distance between them. If any of the inputs are not valid (e.g., non-numeric values), the function should return an error message.
  assert calculate_distance(3, 4, -9, -2) == 13.0
  assert calculate_distance(0, 0, 0, 0) == 0.0
  assert calculate_distance(1, 2, 3, 4) == 2.8284271247461903
  assert calculate_distance(1, 1, "a", "b") == "Invalid input"
output: def calculate_distance(x1, y1, x2, y2):
      if not (isinstance(x1, (int, float)) and isinstance(y1, (int, float)) and isinstance(x2, (int, float)) and isinstance(y2, (int, float))):
          return "Invalid input"
      return ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5