Hawawa College Student-chan Goes to Hawaii~
InterviewTime limit1sMemory limit256 MB
Count the ways to start at island 1 and visit all n islands exactly once using steps +1, +2, or -1 to new islands, modulo 1,000,000,009.
- Level
Medium7 of 10
- Topics
- Dynamic programming, Math, Recursion
- Solved
- No attempts yet
Problem
Hawawawa... The college student Raga likes the phrase "hawawa," you see. Raga, who always says "hawawa" at the end of every sentence, has decided to take a trip to Hawaii, which sounds similar to her beloved hawawa! Hawawawawa... So Raga is looking at Google Maps and making plans for a Hawaii trip...
Because Hawaii is an island chain, Raga travels along the chain and visits every island... Hawawawa... An island chain means islands that formed along a line of heat, and for convenience we say that Hawaii's n islands are arranged in a single row... In this case, the trip must start at the first island, and there are three ways to travel along the chain...
- After seeing some island, you can go straight to the very next island...
- After seeing some island, you can skip one island and go to the island after that...
- After seeing some island, you can go to the previous island...
Hawawa... Raga wants to see all n islands of Hawaii... Also, since Raga gets bored easily, she does not want to visit an island she has already visited... Given n islands, find how many ways Raga can travel through Hawaii...
Hawawawa... But you ask why I'm writing in this style when I'm not even Raga? Hawawa, Raga's friend-chan has caught the speech style too...
Input
The first line gives the number of islands n in the Hawaii chain (1 ≤ n ≤ 50,000), hawawa. Hawawa! Since the answer can be large, print it modulo 1,000,000,009!
Output
On the first line, print the number of ways Raga can travel, hawawa.