#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll const m = 998244353;
ll mpow(ll a, ll n) {
	ll ret = 1;
	while (n) {
		if (n & 1) ret = (ret * a) % m;
		a = (a * a) % m;
		n >>= 1;
	}
	return ret;
}
int main () {
	int X, Y, Z, W;
	cin >> X >> Y >> Z >> W;
	if (W == 0) {
		swap(X, Y); swap(Z, W);
	}
	int dx = X - Z - 1, dy = Y - W;
	ll ans = dx + 1;
	for (int i = 1; i <= dx + dy; i ++) {
		ans = (ans * i) % m;
	}
	std::vector<ll> kai(X + Y, 1), fkai(X + Y);
	for (int i = 1; i < X + Y; i ++) {
		kai[i] = (kai[i - 1] * i) % m;
	}
	fkai[X + Y - 1] = mpow(kai[X + Y - 1], m - 2);
	for (int i = X + Y - 1; i > 0; i --) {
		fkai[i - 1] = (fkai[i] * i) % m;
	}
	ll cb1 = ((kai[X] * fkai[dx + 1]) % m * fkai[Z]) % m;
	ll cb2 = ((kai[Y] * fkai[dy + 1]) % m * fkai[W]) % m;
	ans = (ans * cb1) % m;
	ans = (ans * cb2) % m;
	cout << ans << endl;
}