#include <algorithm>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    int n, m;

    cin >> n >> m;
    vector<vector<int>> array(n, vector<int>(m, 0));

    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) {
            cin >> array[i][j];
            if (array[i][j] == 0)
                array[i][j] = -1000;
        }

    int ans = 0x80000000;

    for (int i = 0; i < n; i++) {
        vector<int> dp(m, 0);
        // 壓縮二維陣列(把 i ~ n 的陣列壓成一維)
        // 就可以當作最大連續和(一維)問題計算
        for (int j = i; j < n; j++) {
            int sum_now = 0;

            for (int k = 0; k < m; k++) {
                dp[k] += array[j][k];

                // 當前和 >=0，那就試著加入下一個
                if (sum_now >= 0)
                    sum_now += dp[k];
                // 當前和<0，那就當作第一個重新開始
                else
                    sum_now = dp[k];

                ans = max(sum_now, ans);
            }
        }
    }

    cout << max(ans, 0) << "\n";
    return 0;
}