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

using mint = modint998244353;

int main(){
    int h,w,a,b;
    cin >> h >> w >> a >> b;
    mint ans0 = 0;
    for(int i1 = 0;i1 < h-a+1;i1++){
        for(int i2 = 0;i2 < h-a+1;i2++){
            int l = max(i1,i2);
            int r = min(i1+a,i2+a);
            if(r-l <= 0) continue;
            ans0 += mint(r-l)/((h-a+1)*(h-a+1));
        }
    }
    mint ans1 = 0;
    for(int j1 = 0;j1 < w-b+1;j1++){
        for(int j2 = 0;j2 < w-b+1;j2++){
            int l = max(j1,j2);
            int r = min(j1+b,j2+b);
            if(r-l <= 0) continue;
            ans1 += mint(r-l)/((w-b+1)*(w-b+1));
        }
    }
    mint ans = ans0*ans1;
    ans = 2*mint(a)*mint(b)-ans;
    cout << ans.val() << endl;
}