Cambodia is located in Southeast Asia, and is also known as Kampuchea. Cambodia is bordered by Laos, Vietnam, Thailand, and the Gulf of Thailand, and covers over 69,000 square miles. Dense forests covers more that half of Cambodia, and only 21 percent of the land is cultivated. The Mekong river, the longest in southeast Asia, and the tenth largest in the world flows through Cambodia, and is navigable for much of its course. Cambodia has a tropical monsoon climate, and an average annual temperature of about 80 degrees (F). December and January are the coolest months, March and April are the hottest months, and the rainy season extends from May to October. Cambodia has a population of over 12 million people according to a 2001 estimate. Population growth is estimated at 2.3 percent per year, although they also have a high infant mortality rate. During the late 1970s, many of Cambodia's towns were depopulated under the rule of the Khmer Rouge, and residents were forced to move to rural areas. A process of re-urbanization was begun in the 1980's. The majority (over 90 percent) of Cambodians are Buddhist, and speak the Cambodian language, also known as Khmer. Approximately 35 percent of Cambodian adults are literate, and public education is free and mandatory for the first six years. A small percentage of children attend secondary school, however 80 percent of Cambodia's people live in rural areas where their principle occupation is farming. The Cambodian diet consists primarily of rice and fish.