#include <bits/stdc++.h>
#include <atcoder/all>
#define OVERLOAD_REP(_1, _2, _3, name, ...) name
#define REP1(i,n) for (auto i = std::decay_t<decltype(n)>{}; (i) != (n); ++(i))
#define REP2(i,l,r) for (auto i = (l); (i) != (r); ++(i))
#define rep(...) OVERLOAD_REP(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
using namespace std;
using namespace atcoder;
using ll = long long;
using ull = unsigned long long;
using P = pair<int,int>;
using LP = pair<long long,long long>;
using SP = pair<string,string>;
using vi = vector<int>;
using vl = vector<long long>;
using vs = vector<string>;
using vc = vector<char>;
using mint1 = modint1000000007;
using mint9 = modint998244353;
const int INF = 2e9;
const long long LINF = 4e18;
const int di[] = {0,1,0,-1,-1,1,-1,1};
const int dj[] = {1,0,-1,0,1,1,-1,-1};
template<class T> inline bool chmin(T& a, T b){if(a>b){a=b;return true;}return false;}
template<class T> inline bool chmax(T& a, T b){if(a<b){a=b;return true;}return false;}
void YesNo (bool ok , const string &s , const string &t) {if(ok) cout << s << endl; else cout << t << endl;} 


//-----def end-----//

using mint = modint998244353;
 const long long mod = 998244353;
 
 struct combination {
   vector<mint> fact, ifact;
   combination(int n):fact(n+1),ifact(n+1) {
     assert(n < mod);
     fact[0] = 1;
     for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
     ifact[n] = fact[n].inv();
     for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
   }
   mint operator()(int n, int k) {
     if (k < 0 || k > n) return 0;
     return fact[n]*ifact[k]*ifact[n-k];
   }
 };

int main () {
    long long x , y , z , w;
    cin >> x >> y >> z >> w;
    combination c(700005);
    mint res = c(x,z)*c(y,w)*c.fact[x+y-z-w-1];
    if(z == 0) res *= x;
    else res *= y;
    cout << res.val() << endl;
	return 0;
}