#include<bits/stdc++.h>
using namespace std;
using ll=long long;
constexpr int MOD=998244353;

namespace Lib{
  ll modpow(ll a,ll n){
    long long ret=1,t=a;
    while(n>0){
      if(n&1)ret=ret*t%MOD;
      t=t*t%MOD;
      n/=2;
    }
    return ret;
  }
}

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll H,W,A,B;
  cin>>H>>W>>A>>B;
  ll t=2*A*B;
  ll Hall=(H-A+1)*(H-A+1)%MOD,Hsum=0;
  ll Wall=(W-B+1)*(W-B+1)%MOD,Wsum=0;
  for(ll i=0;i<H;i++){
    ll x=min(H-A,i)-max(0ll,i-A+1)+1;
    Hsum=(Hsum+x*x)%MOD;
  }
  for(ll i=0;i<W;i++){
    ll x=min(W-B,i)-max(0ll,i-B+1)+1;
    Wsum=(Wsum+x*x)%MOD;
  }
  ll ans=(t-Hsum*Lib::modpow(Hall,MOD-2)%MOD*Wsum%MOD*Lib::modpow(Wall,MOD-2))%MOD;
  if(ans<0)ans+=MOD;
  cout<<ans<<'\n';
}