#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;
	}
	cout << ans << endl;
}