input: Write a function to calculate the square root of a user-defined positive number. The function should return the square root as a floating-point number. If the input is not a positive number, the function should return -1.
  
  assert calculate_square_root(100) == 10.0
  assert calculate_square_root(0) == -1
  assert calculate_square_root(-10) == -1
  assert calculate_square_root(25) == 5.0
  assert calculate_square_root(4) == 2.0
output: def calculate_square_root(num):
      if num < 0:
          return -1
      return num ** 0.5