#include<cstdio>

 #include<cstring>

 #include<algorithm>

 #define LL long long

 #define N 1000

 #define rg register

 using namespace std;

 int n,m,x;

 LL ans,sum[N][N];

 inline int read(){

     int k=,f=; char c=getchar();

     while(c<''||c>'')c=='-'&&(f=-),c=getchar();

     while(''<=c&&c<='')k=k*+c-'',c=getchar();

     return k*f;

 }

 int main(){

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

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

         for(rg int j=;j<=m;j++) x=read(),sum[i][j]=sum[i][j-]+x;

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

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

             LL tmp=;

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

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

                 if(tmp<) tmp=;

                 else ans=max(ans,tmp);

             }

         }

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

     return ;

 }