题目描述
Your task is to calculate the number of arrays such that:
- each array contains $n$ elements;
- each element is an integer from $1$ to $m$;
- for each array, there is exactly one pair of equal elements;
- for each array $a$, there exists an index $i$ such that the array is strictly ascending before the $i$-th element and strictly descending after it (formally, it means that $a_j < a_{j + 1}$, if $j < i$, and $a_j > a_{j + 1}$, if $j \ge i$).
Input
The first line contains two integers $n$ and $m$ ($2 \le n \le m \le 2 \cdot 10^5$).
Output
Print one integer — the number of arrays that meet all of the aforementioned conditions, taken 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
6
提示
The arrays in the first example are:
- $[1, 2, 1]$;
- $[1, 3, 1]$;
- $[1, 4, 1]$;
- $[2, 3, 2]$;
- $[2, 4, 2]$;
- $[3, 4, 3]$.