input: Write a function to calculate the square root of a user-defined positive number. If the given number is negative, return -1.
  import math
  
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(25)==5.0
  assert calculate_square_root(9)==3.0
  assert calculate_square_root(4)==2.0
  assert calculate_square_root(-1)==-1
output: def calculate_square_root(num):
      if num < 0:
          return -1
      return math.sqrt(num)