#include<bits/stdc++.h>
#include<atcoder/modint>
using namespace std;
#ifdef LOCAL
#include <debug_print.hpp>
#define OUT(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define OUT(...) (static_cast<void>(0))
#endif
int main(){
  int H, W, A, B;
  cin >> H >> W >> A >> B;
  assert(1 <= H && H <= 2e5);
  assert(1 <= W && W <= 2e5);

  using modint = atcoder::modint998244353;
  modint xs = 0, ys = 0;
  for(int x = 0; x < H; x++){
    modint prob = modint(max<int>(x - A + 1, 0) + max<int>(0, H - A - x)) / (H - A + 1);
    xs += (1 - prob) * (1 - prob);
  }
  for(int y = 0; y < W; y++){
    modint prob = modint(max<int>(y - B + 1, 0) + max<int>(0, W - B - y)) / (W - B + 1);
    ys += (1 - prob) * (1 - prob);
  }

  cout << (modint(2) * A * B - xs * ys).val() << endl;
}