#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
// #include <atcoder/modint>
// #include <atcoder/math>
// #include <atcoder/segtree>
// #include <atcoder/lazysegtree>
// #include <atcoder/dsu>
// #include <atcoder/scc>
using namespace atcoder;

// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

typedef long long int ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<vvll> vvvll;
typedef vector<pll> vpll;
typedef vector<vpll> vvpll;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef priority_queue<pll, vpll, function<bool(pll,pll)> > pqpll; 
typedef priority_queue<ll, vll, function<bool(pll,pll)> > pqll;
 
struct edge{ ll to, cost; edge(ll e_to,ll e_cost): to(e_to), cost(e_cost){} };
typedef vector<vector<edge>> Graph;
 
#define rep(i,a,n) for(ll i = a;i < n;i++)
#define rrep(i,a,n) for(ll i = n-1; i >= a;i--)
#define LINF (1LL << 60)
#define INF (1 << 30)
#define fs first
#define sc second
#define EPS (ld)1e-10
#define ALL(a) a.begin(), a.end()
#define tcheck(a) if((clock() - start)/(ld)CLOCKS_PER_SEC >= a) break
#define debug(s) cout << #s << endl
#define debugval(x) cout << #x" = " << x << endl
 
template<typename T> ll sz(vector<T> &pos){ return (ll)pos.size(); }
template<typename T> ll sz(priority_queue<T, vector<T> > &que) {return (ll)que.size(); }
template<typename T> ll sz(priority_queue<T, vector<T>, greater<T> > &que) {return (ll)que.size(); }
ll sz(string &s) {return (ll)s.size(); } 
 
template<typename T> void chmin(T &a, T b) { if(a > b) a = b; }
template<typename T> void chmax(T &a, T b) { if(a < b) a = b; }

// __int128_t gcd(__int128_t a, __int128_t b){ return ((!b) ? a : gcd(b,a%b)); } 
ll gcd(ll a,ll b){ return ((!b) ?a :gcd(b, a%b)); }
ll lcm(ll a,ll b){ return a / gcd(a,b) * b; }
ll dx[4] = {0,-1,0,1},dy[4] = {-1,0,1,0};
// ll dx[8] = {0,-1,-1,-1,0,1,1,1},dy[8] = {-1,-1,0,1,1,1,0,-1};
inline bool isinside(ll i,ll n){ return (i < n && i >= 0); }

using mint = modint998244353;
int main(){
    ll h,w,a,b;
    cin >> h >> w >> a >> b;

    auto calc = [](ll h, ll a) -> mint {
        mint res = 0;
        rep(i,0,h-a+1){ //[i, i+a)
            mint temp = 0;
            //i以降
            if(i+a < h-a+1) temp += mint(a)*mint(a+1)/mint(2);
            else{
                //[j,j+a) = [j, h) -> j = h-a -> [h-a, i+a) -> i+2*a-h
                ll cnt = a - (i+2*a-h) + 1;
                temp += mint(cnt)*mint(a+(i+2*a-h))/mint(2);
            }

            //iより前
            ll j = h-a-i;
            if(j+a < h-a+1) temp += mint(a)*mint(a+1)/mint(2) - mint(a);
            else{
                ll cnt = a - (j+2*a-h) + 1;
                temp += mint(cnt)*mint(a+(j+2*a-h))/mint(2);
                temp -= mint(a);
            }

            res += temp/mint(h-a+1).pow(2);
        }

        return res;
    };

    cout << (mint(2)*mint(a)*mint(b) - calc(h,a)*calc(w,b)).val() << endl; 
}