#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;

template <typename mint>
struct combination {
  vector<mint> fact,factinv;

  combination(int n) {
    fact.resize(n+1);
    factinv.resize(n+1);
    fact[0]=1;
    for (int i=1;i<=n;i++) {
      fact[i]=fact[i-1]*i;
    }
    for (int i=0;i<=n;i++) {
      factinv[i]=fact[i].inv();
    }
  }

  mint nCr(long long n,long long r) {
    if (n<0||r<0||n-r<0) {
      return 0;
    }
    return fact[n]*factinv[r]*factinv[n-r];
  }
  
  mint nPr(long long n,long long r) {
    if (n<0||r<0||n-r<0) {
      return 0;
    }
    return fact[n]*factinv[n-r];
  }
};

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  using mint=modint998244353;
  int x,y,z,w;
  cin>>x>>y>>z>>w;
  combination<mint> c(x+y);
  cout<<(c.nCr(x,z)*c.nCr(y,w)*c.fact[x+y-z-w-1]*(z==0?x:y)).val()<<endl;
}