#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i, n) for(int i=0;i<(n);++i)
#define rep1(i, n) for(int i=1;i<=(n);i++)
#define ll long long
using mint = modint998244353;
using P = pair<ll,ll>;
using lb = long double;
using T = tuple<ll, ll, ll>;
#ifdef LOCAL
#  include <debug_print.hpp>
#  define dbg(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define dbg(...) (static_cast<void>(0))
#endif

int main()
{
    int h, w, A, B;
    cin >> h >> w >> A >> B;
    vector<int> a(h+1), b(w+1);
    rep(i,h-A+1){
        a[i]+=1;    
        a[i+A]-=1;
    }
    rep(i,w-B+1){
        b[i]+=1;    
        b[i+B]-=1;
    }
    rep(i,h) a[i+1]+=a[i];
    rep(i,w) b[i+1]+=b[i];
    mint ans = 0;
    mint sum = 0;
    mint sqsum = 0;
    dbg(a,b);
    rep(i,w) {
        sum += b[i];
        sqsum += mint(b[i])*mint(b[i]);
    }
    mint all = mint(h-A+1)*mint(w-B+1);
    dbg(sum.val(),all.val(),sqsum.val());
    rep(i,h){ 
        ans += mint(a[i])*mint(a[i]) * sqsum + 2 * mint(a[i])*sum*all - 2*mint(a[i])*mint(a[i]) * sqsum;
    }
    dbg(ans.val());
    ans/=all;
    ans/=all;
    cout<<ans.val()<<endl;
    return 0;
}