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 n = in.nextInt();
        if(n == 1){
            System.out.println(1);
            return;
        }
        Long[] dp = new Long[n];
        dp[0] = 1L;
        dp[1] = 2L;

        for(int i = 2; i < n; i++){
		  // 每次都取模
            dp[i] = (dp[i - 1] + dp[i - 2]) % 998244353;
        }
        Long res = dp[n - 1];
        System.out.println(res);
    }
}