#include <bits/stdc++.h>

const int N = ;

int sum[N][N];

int n, m;

#define gc getchar()

inline int read() {

    int x = , f = ; char c = gc;

    while(c < '' || c > '') {if(c == '-') f = -; c = gc;}

    while(c >= '' && c <= '') x = x *  + c - '', c = gc;

    return x * f;

}

int main() {

    m = read(), n = read();

    for(int i = ; i <= n; i ++) {

        for(int j = ; j <= m; j ++) {

            int x = read();

            sum[i][j] = sum[i][j - ] + x;

        }

    }

    int Ans();

    for(int i = ; i <= m; i ++) {

        for(int j = i; j <= m; j ++) {

            int Now(), Max();

            for(int k = ; k <= n; k ++) {

                Now += sum[k][j] - sum[k][i - ];

                if(Now < ) Now = ;

                Max = std:: max(Max, Now);

            }

            Ans = std:: max(Ans, Max);

        }

    }

    printf("%d", Ans);

    return ;

}