#include<iostream>
#include<vector>
#include<cassert>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
vector<int>f(int H,int K)
{
	vector<int>ret;
	if(H<=2*(K-1))
	{
		for(int i=1;i<=H;i++)
		{
			int l=max(1,i-K+1),r=min(i,H-K+1);
			ret.push_back(r-l+1);
		}
	}
	else
	{
		for(int i=1;i<K;i++)
		{
			ret.push_back(i);
			ret.push_back(i);
		}
		int r=H-2*(K-1);
		ret.push_back(-r);
	}
	return ret;
}
int H,W,N,K;
mint C[1<<20];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin>>H>>W>>N>>K;
	vector<int>h=f(H,K),w=f(W,K);
	for(int hi:h)for(int wi:w)
	{
		if(hi>=0)
		{
			if(wi>=0)C[hi*wi]++;
			else C[hi*K]-=wi;
		}
		else
		{
			if(wi>=0)C[K*wi]-=hi;
			else C[K*K]+=(long)hi*wi;
		}
	}
	mint ans=(long)H*W;
	mint t=(long)(H-K+1)*(W-K+1);
	mint invt=t.inv();
	for(int c=1;c<=K*K;c++)
	{
		ans-=(1-mint::raw(c)*invt).pow(N)*C[c];
	}
	cout<<ans.val()<<endl;
}