input: 
  from typing import List
  
  def concatenate_strings(strings: List[str], separator: str) -> str:
      """ Take a list of strings and concatenate them using the provided separator.
      >>> concatenate_strings(["Sample", "Text", "Hello"], "-")
      "Sample-Text-Hello"
      >>> concatenate_strings(["A", "B", "C"], ",")
      "A,B,C"
      """
  
output:     result = ""
      for i, s in enumerate(strings):
          result += s
          if i < len(strings) - 1:
              result += separator
      return result