#include<bits/stdc++.h>
typedef long long ll;
#define f(i,n) for(ll i=0;i<n;i++)
#define ggr getchar();getchar();return 0;
#define P pair<ll,ll>
#define F first
#define S second
#define mod 1000000007
#define Mod 998244353
#define all(v) v.begin(), v.end()
#define INF LLONG_MAX/3
#define pi 3.14159265359
using namespace std;
ll k[300000];
int mypow(ll a,ll b,ll c) {
	if (b == 0)return 1;
	if (b % 2)return mypow(a, b - 1, c)*a%c;
	ll fa = mypow(a, b / 2, c);
	return fa * fa%c;
}
int nCr(int a, int b) {
	return k[a] * mypow(k[b], Mod - 2, Mod) % Mod * mypow(k[a - b], Mod - 2, Mod) % Mod;
}
int main() {
	ll a, b, c, d, ans = 0;
	cin >> a >> b >> c >> d;
	ll z = d - (a - 1)*(c - 1), x = b - d;
	k[0] = 1;
	f(i, max(a,z)) {
		k[i + 1] = k[i] * (i + 1);
	}
	for (; z >= a - 1; z--) {
		ans += nCr(z-1, a - 2)*x%Mod;
		ans %= Mod;
		x++;
	}
	cout << ans * k[a] % Mod << endl;
	ggr;
}