#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
using ll = long long;

ll my_pow(ll x, ll n, ll mod) {
    ll ret;
    if (n == 0) {
        ret = 1;
    } else if (n % 2 == 1) {
        ret = (x * my_pow((x * x) % mod, n / 2, mod)) % mod;
    } else {
        ret = my_pow((x * x) % mod, n / 2, mod);
    }
    return ret;
}

ll inv(ll x, ll mod) { return my_pow(x, mod - 2, mod); }

ll mod = 998244353;

int main() {
    ll X, Y, Z, W;
    cin >> X >> Y >> Z >> W;

    vector<ll> fact(600005);
    fact[0] = 1;
    for (ll i = 0; i < 600004; i++) {
        fact[i + 1] = (fact[i] * (i + 1)) % mod;
    }

    if (Z == 0) {
        swap(X, Y);
        swap(Z, W);
    }
    ll ans =
        (fact[X] * ((inv(fact[X - Z], mod) * inv(fact[Z], mod)) % mod)) % mod;
    ans = (ans * Y) % mod;
    ans = (ans * fact[X + Y - Z - W - 1]) % mod;
    cout << ans << endl;
}