#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<ll,ll>;
#define fix(x) fixed << setprecision(x)
#define asc(x) x, vector<x>, greater<x>
#define rep(i, n) for(ll i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);
const int MAX_N = 1001000;
vector<ll> fac(MAX_N), finv(MAX_N), inv(MAX_N);
void init(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i=2;i<MAX_N;i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll mcomb(int n,int k){
    if (n<k) return 0;
    if (n<0 || k<0) return 0;
    return fac[n] * (finv[k] * finv[n-k] % MOD) % MOD;
}
ll mperm(int n,int k){
    if (n<k) return 0;
    if (n<0 || k<0) return 0;
    return fac[n] * finv[n-k] % MOD;
}
int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    init();
    ll x,y,z,w;
    cin >> x >> y >> z >> w;
    ll k = (z?y-w:x-z);
    cout << mcomb(x+y-z-w-1, k-1)*mperm(x,x-z)%MOD*mperm(y,y-w)%MOD << '\n';
    return 0;
}