#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
const int mod=998244353;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){assert(!a.empty());T ans=a[0]-a[0];for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}

ll jyo(ll x,ll y,ll z){
  ll H=y; //ここから
       ll a=1,b=(x%z+z)%z,c=1;
       while(H>0){
         a*=2;
         if(H%a!=0){
           H-=a/2;
           c*=b;
           c%=z;
         }
        b*=b;
         b%=z;
      } //ここまで
 return c;
}



void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,0,t) solve();
}

void solve(){
	ll H,W,N,K;
    cin>>H>>W>>N>>K;
    ll S=(H-K+1)*(W-K+1)%mod;
    ll Sr=jyo(S,mod-2,mod);
    ll ans=0;
    auto f=[&](ll a)->ll {
        a%=mod;
        return (1-jyo((S-a)*Sr%mod,N,mod))%mod;
    };
    auto g=[&](ll a)->vector<ll> {
        vector<ll> res;
        if(a<2*K){
            rep(i,0,a) res.push_back(i);
        }
        else{
            rep(i,0,K) res.push_back(i);
            rep(i,0,K) res.push_back(a-K+i);
        }
        return res;
    };
    auto h=[&](ll a,ll b)->ll {
        return min(b-K+1,a+1)-max(0ll,a-K+1);
    };
    auto p=g(H),q=g(W);
    for(auto x:p) for(auto y:q){
        ans+=f(h(x,H)*h(y,W));
    }
    for(auto x:p){
        ans+=f(h(x,H)*K)*(W-(int)q.size())%mod;
    }
    for(auto y:q){
        ans+=f(h(y,W)*K)*(H-(int)p.size())%mod;
    }
    ans+=f(K*K)*((W-(int)q.size())*(H-(int)p.size())%mod)%mod;
    cout<<(ans%mod+mod)%mod<<"\n";
}