[BOJ] 10844. 쉬운 계단수

import java.util.Scanner;

public class Main {
	static final long mod = 1000000000l;
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int N = sc.nextInt();
		long[][] dp = new long [N+1][10];
		
		for(int i = 1; i <= 9; i++) {
			dp[1][i] = 1;
		}
		
//		dp[n][i] : 길이가 n이면서 i로 끝나는 계단 수의 개수.
		for(int i = 2; i <= N; i++) {
			for(int j = 0; j <= 9; j++) {
				if(j-1 < 0) dp[i][j] = dp[i-1][j+1];
				else if(j+1 > 9) dp[i][j] = dp[i-1][j-1]; 
				else dp[i][j] = dp[i-1][j-1] + dp[i-1][j+1];
				dp[i][j] %= mod;
			}
		}
		
		long answer = 0l;

		for(int i = 0; i <= 9; i++) {
			answer = answer + dp[N][i];
			answer = answer % mod;
		}
		
		System.out.println(answer);		
	}
}