#include<bits/stdc++.h>
 
using namespace std;
 
int main() {
    ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
    int n, m; cin >> n >> m;
    vector<vector<int> > a(n, vector<int>(m));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            cin >> a[i][j];
            if (j > 0) a[i][j] += a[i][j - 1]; // prefix sum for i-th row
        }
    }
    int ans = 0;
    for (int i = 0; i < m; i++) { // fix i
        for (int j = i + 1; j < m; j++) { // fix j
            int sum = 0;
            for (int k = 0; k < n; k++) { // iterate from first row
                sum += a[k][j];
                if (i > 0) sum -= a[k][i - 1];
                ans = max(ans, sum);
                if (sum < 0) sum = 0;
            }
        }
    }
    cout << ans;
    return 0;
}

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

NCA0CjAgLTIgLTcgMAo5IDIgLTYgMgotNCAxIC00IDEKLTEgOCAwIC0y

4 4
0 -2 -7 0
9 2 -6 2
-4 1 -4 1
-1 8 0 -2