#include<cstdio>

 #include<cstring>

 #include<vector>

 #include<algorithm>

 #define CLR(a,b) memset((a),(b),sizeof((a)))

 using namespace std;

 const int N = ;

 int dp[N][N];

 int main(){

     int n, m, i, j, k, s, ans, x;

     scanf("%d%d", &m, &n);

     CLR(dp, );

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

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

             scanf("%d", &x);

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

         }

     }

     ans = ;

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

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

             s = ;

             for(k = ; k <= m; ++k){

                 x = dp[j][k] - dp[i-][k];

                 if(s > )

                     s += x;

                 else

                     s = x;

                 ans = max(ans, s);

             }

         }

     }

     printf("%d\n", ans);

     return ;

 }