题目描述
Problem Statement
Find the number of sequences of integers with $N terms, A=(a_1,a_2,\ldots,a_N)$, that satisfy the following conditions, modulo 998244353.
- $0 \leq a_1 \leq a_2 \leq \ldots \leq a_N \leq M$.
- For each $i=1,2,\ldots,N-1$, the remainder when a_i is divided by 3 is different from the remainder when a_{i+1} is divided by 3.
Input
The input is given from Standard Input in the following format:
N M
Output
Print the answer.
Constraints
- $2 \leq N \leq 10^7$
- $1 \leq M \leq 10^7$
- All values in the input are integers.
Sample Input 1
3 4
Sample Output 1
8
Here are the eight sequences that satisfy the conditions.
- (0,1,2)
- (0,1,3)
- (0,2,3)
- (0,2,4)
- (1,2,3)
- (1,2,4)
- (1,3,4)
- (2,3,4)
Sample Input 2
276 10000000
Sample Output 2
909213205
Be sure to find the count modulo 998244353.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
3 4
样例输出
8