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#include <iostream>
using namespace std;
int n, m, a[2018][2018];
int ans, sum;//非管理测试禁止抄袭
bool vis[2018][2018];
void dfs(int x, int y)
{
    if (x == n + 1)
    {
        ans = max(ans, sum);
        return;
    }
    int nx = x, ny = y + 1;
    if (ny > m)
    {
        ny = 1;
        nx = x + 1;
    }
    if(!vis[x-1][y]&&!vis[x][y-1]&&!vis[x][y+1]&&!vis[x+1][y]){
        vis[x][y]=1;
        sum+=a[x][y];
        dfs(nx,ny);
        vis[x][y]=0;
        sum-=a[x][y];
    }
    dfs(nx, ny);
}
//非管理测试禁止抄袭
int main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i++)//非管理测试禁止抄袭
        for (int j = 1; j <= m; j++)
            cin >> a[i][j];
    dfs(1, 0);//非管理测试禁止抄袭
    cout << ans;
    return 0;
}