#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
    int n,m,ans=0;
    cin>>n>>m;
    int a[n+1][m+1];
    for (int i=1;i<=n;i++)
    {
        for (int j=1;j<=m;j++)
        {
            cin>>a[i][j];
        }
    }
    for (int i=2;i<=n;i++)
    {
        for (int j=2;j<=m;j++)
        {
            a[i][j]=a[i-1][j]+a[i][j-1]-a[j-1][i-1]+a[i][j];
        }
    }
    for (int i=1;i<=n;i++)
    {
        for (int j=1;j<=m;j++)
        {
            if (a[i][j]>ans)
            {
                ans=a[i][j];
            }
        }
    }
    cout<<ans;
    return 0;
}