#include <iostream>
using namespace std;
 
const int f = 2000;
long long a[f][f];
 
int main() {
    int m, n;
    cin >> m >> n;
 
    for (int i = 0; i < m; i++)
        for (int j = 0; j < n; j++)
            cin >> a[i][j];
 
    long long v = -1e18;
 
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++) {
            long long h = 0;
            int x = i, y = j;
            while (x < m && y < n)
                h += a[x++][y++];
            x = i - 1; y = j + 1;
            while (x >= 0 && y < n)
                h += a[x--][y++];
 
            v = max(v, h);
        }
    }
 
    cout << v << endl;
    return 0;
}
 

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3 4 
1 1 1 0
1 0 1 1
0 0 1 1