#include<iostream>
#include<algorithm>
using namespace std;

const int N = 105;

int m, n, g[N][N], dp[N*2][N][N];

inline bool good(int i, int j){
    return j >= 0 and i - j >= 0 and j < m and i - j < n and g[j][i - j] != -1;
}

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> m >> n;
    for(int i = 0; i < m; ++i){
        for(int j = 0; j < n; ++j){
            cin >> g[i][j];
        }
    }
    // from (0, 0) to (m-1, n-1)
    for(int i = 0; i <= m + n - 2; ++i){
        for(int j = 0; j <= i; ++j){
            if(!good(i, j)) continue;
            for(int k = 0; k <= i; ++k){
                if(!good(i, k)) continue;
                dp[i][j][k] = g[j][i - j] + (j != k ? g[k][i - k] : 0);

                int mx = 0;
                if(good(i-1, j) and good(i-1, k))
                    mx = max(mx, dp[i-1][j][k]);
                if(good(i-1, j) and good(i-1, k-1))
                    mx = max(mx, dp[i-1][j][k-1]);
                if(good(i-1, j-1) and good(i-1, k))
                    mx = max(mx, dp[i-1][j-1][k]);
                if(good(i-1, j-1) and good(i-1, k-1))
                    mx = max(mx, dp[i-1][j-1][k-1]);
                dp[i][j][k] += mx;
            }
        }
    }
    cout << dp[m + n - 2][m-1][m-1];
    return 0;
}