1312D.cpp

#include <iostream>

using namespace std;

const long long MOD = 998244353;

unsigned long long power(unsigned long long x,
                                  int y, int p){
    unsigned long long res = 1;
    x = x % p;
    while (y > 0){
        if (y & 1)
            res = (res * x) % p;
        y = y >> 1;
        x = (x * x) % p;
    }
    return res;
}
unsigned long long modInverse(unsigned long long n, 
                                            int p){
    return power(n, p - 2, p);
}
unsigned long long nCrModPFermat(unsigned long long n,
                                 int r, int p){
    if (n < r)
        return 0;
    if (r == 0)
        return 1;
    unsigned long long fac[n + 1];
    fac[0] = 1;
    for (int i = 1; i <= n; i++)
        fac[i] = (fac[i - 1] * i) % p;
 
    return (fac[n] * modInverse(fac[r], p) % p
            * modInverse(fac[n - r], p) % p)
           % p;
}
 


int main(){
	unsigned long long n, m;
	cin >> n >> m;
	unsigned long long p = nCrModPFermat(m, n - 1, MOD);
	unsigned long long res = (((p * power(2, n - 3, MOD)) % MOD) * (n - 2)) % MOD;
	cout << res;
}