题目描述
Problem Statement
A positive-integer sequence is said to be splendid if no two adjacent elements are equal.
Find the sum, modulo 998244353, of the lengths of all splendid sequences whose elements have a sum of N.
Input
The input is given from Standard Input in the following format:
N
Output
Print the answer.
Constraints
- $1 \le N \le 2 \times 10^5$
- All values in the input are integers.
Sample Input 1
4
Sample Output 1
8
There are four splendid sequences whose sum is 4: (4),(1,3),(3,1),(1,2,1). Thus, the answer is the sum of their lengths: 1+2+2+3=8.
(2,2) and (1,1,2) also have a sum of 4 but ineligible because their 1-st and 2-nd elements are the same.
Sample Input 2
297
Sample Output 2
475867236
Sample Input 3
123456
Sample Output 3
771773807
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分