题解 | 数楼梯

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int num = in.nextInt();
        if(num <= 2) {
            System.out.println(num);
            return;
        }
        long[] arr = new long[num + 1];
        arr[1] = 1;
        arr[2] = 2;
        for (int i = 3; i <= num; i++) {
            arr[i] =(arr[i - 1] + arr[i - 2]) % 998244353L;
        }
        System.out.println(arr[num]);
    }
}