input: 
  from flask import Flask
  import datetime
  
  def current_datetime_api() -> str:
      """Creates a web API using Flask to provide the current date and time. 
      The API should return the current date and time in the format "YYYY-MM-DD HH:MM:SS".
      >>> current_datetime_api()
      '2023-10-01 12:34:56'  # Example output, actual time will vary.
      """
  
output:     
      app = Flask(__name__)
  
      @app.route('/')
      def get_current_datetime():
          now = datetime.datetime.now()
          return now.strftime("%Y-%m-%d %H:%M:%S")
  
      if __name__ == '__main__':
          app.run()
  