#include <cstdio>
using namespace std;

int map[1001][1001],f[1001][1001];

int main(void)
{
	freopen("aya.in","r",stdin);
	freopen("aya.out","w",stdout);
	int i,j,ii,jj,n,m,r,c,maxnum=0,temp;
	scanf("%d%d%d%d",&n,&m,&r,&c);
	for (i=1;i<=n;i++)
		for (j=1;j<=m;j++)
		{
			scanf("%d",&map[i][j]);
			f[i][j]=map[i][j]+f[i-1][j]+f[i][j-1]-f[i-1][j-1];
		}
	for (i=1,ii=r;ii<=n;i++,ii++)
		for (j=1,jj=c;jj<=m;j++,jj++)
		{
			temp=f[ii][jj]-f[i-1][jj]-f[ii][j-1]+f[i-1][j-1];
			if (maxnum<temp)
				maxnum=temp;
		}
	printf("%d\n",maxnum);
	return(0);
}