#include <bits/stdc++.h>
using namespace std;

const int N=55;
int f[N+N][N][N];
int a[N][N];
int n, m;

int main(){
    memset(a, 0x00, sizeof a);
    memset(f, 0x00, sizeof f);
    cin>>n>>m;

    for(int i=1; i<=n; ++i){
        for(int j=1; j<=m; ++j)
            cin>>a[i][j];
    }

    for(int k=2; k<=n+m; ++k)
        for(int i1=1; i1<=n; ++i1)
            for(int i2=1; i2<=n; ++i2){
                int j1=k-i1;
                int j2=k-i2;
                if(j1>=1 && j1<=m && j2>=1 && j2<=m){
                    int w=a[i1][j1];
                    if(i1!=i2) w+=a[i2][j2];
                    f[k][i1][i2]=max(f[k][i1][i2], f[k-1][i1][i2]+w);
                    f[k][i1][i2]=max(f[k][i1][i2], f[k-1][i1-1][i2]+w);
                    f[k][i1][i2]=max(f[k][i1][i2], f[k-1][i1][i2-1]+w);
                    f[k][i1][i2]=max(f[k][i1][i2], f[k-1][i1-1][i2-1]+w);
                }
            }
    cout<<f[n+m][n][n]<<endl;

    return 0;
}