input: Write a function to calculate the square root of a given positive number. If the given number is negative or zero, return the string "Invalid input". Otherwise, return the square root of the number.
  assert calculate_square_root(100)==10.0
  assert calculate_square_root(25)==5.0
  assert calculate_square_root(0)=="Invalid input"
  assert calculate_square_root(-4)=="Invalid input"
  assert calculate_square_root(9)==3.0
output: def calculate_square_root(num):
      if num <= 0:
          return "Invalid input"
      return num ** 0.5