Yu Ji is very annoying because he always ask others to guess his boring riddles. He will find different guys to guess his riddle for everyday. Unfortunately, he finds you to take this boring job today. Here comes his riddle:

"Suppose there is a convex polygon with N vertexes, and K points inside the polygon, satisfying that no 3 points among these N+K ones are collinear. Then I add some segments connecting these points, such that the segments intersect each other only at these points and the polygon is divided into triangles. Do you know how many triangles there are after doing that? Guess it! "

Is it very boring? Absolutely! However, you still have to figure it out. Why? Let me tell you a story. Long long ago, there was a kid. One day, he was asked to guess a riddle by Yu Ji. He was not able to guess the answer. The next day, he died, His name is: Sun Ce.