#include <bits/stdc++.h>
using namespace std;
const long long MOD = 998244353;
const long long HALF = 499122177;
const long long ONE_THIRD = 332748118;
long long modpow(long long a, long long b){
  long long ans = 1;
  while (b > 0){
    if (b % 2 == 1){
      ans *= a;
      ans %= MOD;
    }
    a *= a;
    a %= MOD;
    b /= 2;
  }
  return ans;
}
long long modinv(long long a){
  return modpow(a, MOD - 2);
}
int main(){
  long long H, W, A, B;
  cin >> H >> W >> A >> B;
  auto solve = [](long long H, long long A){
    long long ans = 0;
    for (int i = -(H - A); i <= H - A; i++){
      ans += max(A - abs(i), (long long) 0) * (H - A + 1 - abs(i)) % MOD;
    }
    ans %= MOD;
    ans *= modpow(modinv(H - A + 1), 2);
    ans %= MOD;
    return ans;
  };
  long long ans = solve(H, A) * solve(W, B) % MOD;
  ans = A * B * 2 - ans + MOD;
  cout << ans % MOD << endl;
}