500
Every year since 1986, some of the world's most daring runners have gathered in the desert of Morocco. They are there to take part in one of the most difficult races in the world. The Marathon of the Sands, as it is called, covers over 125 miles of desert and mountain wilderness. The runners complete the course in fewer than seven days, and they run with their food, clothing, and sleeping bags on their backs. they run 15 miles across a desert of sand, rocks, and thorny bushes. Few runners finish the day without blistered and raw feet. Because they are allowed less than nine quarts of water during each day of the race, they also suffer from a lack of water. Most of all, they are exhausted when they arrive at the campsite for the night.
What is the main idea of this passage?
That the Marathon of the Sands is a very difficult race to run.