input: 
  from typing import List
  
  
  def replace_string(input_string: str, target_string: str, replacement_string: str) -> str:
      """ Replace all occurrences of the target string with the replacement string in the input string.
      >>> replace_string("Hello World!", "World", "Python")
      'Hello Python!'
      >>> replace_string("I love programming in Python.", "Python", "Java")
      'I love programming in Java.'
      """
  
output:     return input_string.replace(target_string, replacement_string)