The Kingdom of Bahrain consists of Bahrain Island and 33 of the 37 Bahrain Islands, lying in the Arabian Gulf's Gulf of Bahrain off the north shore of Asia's Arabian Peninsula. Bahrain's capital city is Manama. The islands are about 24 kilometers  off the east coast of Saudi Arabia and 28 kilometers  from Qatar. The total area of the country is about 780 square kilometers , about 3.5 times the size of the District of Columbia. Bahrain Island accounts for about 83% of the kingdom's land area, comprising 590 square kilometers . It is 48 kilometers  long from north to south and at its widest point stretches 16 kilometers  from east to west. The island is surrounded by several of the Middle East's large petroleum fields and commands a strategic position amid the Persian Gulf's shipping lanes.
Question: How many of the Bahrain islands are not included in the Kingdom of Bahrain?
Answer: 4