input: Write a python function to parse a JSON string and return a dictionary.
  assert parse_json("{\"name\": \"John Doe\", \"age\": 28}") == {"name": "John Doe", "age": 28}
  assert parse_json("{\"city\": \"New York\", \"population\": 8336817}") == {"city": "New York", "population": 8336817}
  assert parse_json("{\"is_valid\": true, \"count\": 5}") == {"is_valid": True, "count": 5}
output: def parse_json(json_string):
      import json
      return json.loads(json_string)