#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

#include <atcoder/modint>
using mint = atcoder::modint998244353;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int x, y, z, w;
  cin >> x >> y >> z >> w;
  if (z == 0) swap(x, y), swap(z, w);
  vector<mint> fact(x + y + z, 1);
  for (int i = 1; i < x + y + z; ++i) fact[i] = fact[i - 1] * i;
  cout << ((fact[x] / fact[x - z] / fact[z]) * y * fact[x + y - z - 1]).val() << '\n';
  return 0;
}