[Silver 1] 10844번 쉬운 계단 수

import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        long[][] dp = new long[n+1][10];
        long ans = 0;
        
        for(int i=1; i<=9; i++) { dp[1][i] = 1; }
        
        for(int i=2; i<=n; i++) {
            for(int j=0; j<=9; j++) {
                if(j==0) { dp[i][j] = dp[i-1][1]%1_000_000_000; }
                else if(j==9) { dp[i][j] = dp[i-1][8]%1_000_000_000; }
                else { dp[i][j] = (dp[i-1][j-1]+dp[i-1][j+1])%1_000_000_000; }
            }
        }
        
        for(int i=0; i<=9; i++) { ans += dp[n][i]; }
        
        System.out.println(ans%1_000_000_000);
    }
}