input: def count_key_switches(input_string: str) -> int:
      """
      You have a 0-indexed string input_string entered by a user. Changing a key is described as pressing a key different from the previously pressed one. For instance, if input_string = "xy" there is one key change, whereas for input_string = "yYyy" there are none.
  
      Return the count of key switches the user made.
  
      Note: Modifiers such as shift or caps lock are not considered as key changes. For example, if a user types 'b' followed by 'B', it will not be counted as a key change.
  
      Examples:
      >>> input_string = "bBcCdD"
      2
      >>> input_string = "BbBbBbBb"
      0
  
      Constraints:
      1 <= input_string.length <= 100
      input_string contains only uppercase and lowercase English letters.
      """
output:     
      if not input_string:
          return 0
  
      count = 0
      previous_char = input_string[0].lower()
  
      for char in input_string[1:]:
          current_char = char.lower()
          if current_char != previous_char:
              count += 1
              previous_char = current_char
  
      return count
  