#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 2000 + 10;
int n, m, r, c, s;
int a[N][N];
int main() {
    freopen("aya.in", "r", stdin);
    freopen("aya.out", "w", stdout);
    scanf("%d %d %d %d", &n, &m, &r, &c);
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++) {
            scanf("%d", a[i]+j);
            a[i][j] += a[i][j-1] + a[i-1][j] - a[i-1][j-1];
        }
    for(int i=r; i<=n; i++)
        for(int j=c; j<=m; j++)
            s = max(s, a[i][j] - a[i-r][j] - a[i][j-c] + a[i-r][j-c]);
    printf("%d\n", s);
    return 0;
}