The Nadam Festival, usually held from June 4 to 9(lunar calendar), is one of the most exciting and colorful festivals in the Inner Mongolian Autonomous Region. At the center of the festivities are the fierce horse racing, archery  and wrestling competitions, the traditional sports of the Mongolian warriors (the three "manly" sports, though young girls and women participate in the horse racing and archery contests). In Mongolian, the word "Nadam" means "amusement and entertainment" and the festival began in 1225 AD, when Genghis Khan organized an expedition to the west and got control of Khwarezm. In order to celebrate the victory they held the magnificent Nadam Fari. The Mongolians used this exciting gathering as a big occasion to compete in the horse racing, Mongolian wrestling and archery, which were regarded as the three basic skills of men. Gradually more and more events were added to the festival, such as marksmanship , chess, reciting epics, polo , film, drama, singing, dancing, track and field competitions and so on. There are three kinds of Nadam, the big one, the medium one and the small one. The big Nadam requires the participation of 512 wrestlers and 300 horses and usually lasts 7-10 days while the medium Nadam will have the participation of 256 wrestlers and 100-150 horses, lasting 5-7 days. And 64 or 128 wrestlers and 30 or 50 horses will take part in the small Nadam, which lasts 3-5 days. Anyone can apply to compete in Nadam, regardless of his or her ethnic origin and religious belief. Nadam has become a popular artistic and sports event participated in by people of all ages. Boys and girls can also take the opportunity to show their love, i. e. the so-called "meeting at aobao". In addition to sports competition, people also make good use of this gathering to hold talks and establish relations in economic trade or to interchange goods. What's the main idea of the passage?
The introduction of the Nadam Festival. The origin of the Nadam Festival. The sports events of the Nadam Festival. The modern style of the Nadam Festival.