#include <bits/stdc++.h>

#define FASTER() ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
#define ff first
#define ss second
#define pb push_back
#define all(a) a.begin(), a.end()
#define dbg(x) cerr<<" "<<#x<<" "<<x<<endl
#define int long long

typedef long long ll;

using namespace std;

signed main() {
    FASTER();
    int n, m;
    cin >> n >> m;
    vector <vector <int>> mt(n, vector <int>(m));
    for(auto &a : mt) {
        for(auto &i : a) {
            cin >> i;
        }
    }
    vector <vector <int>> dp1(n, vector <int>(m)), dp2(n, vector <int>(m));
    dp1[0][0] = mt[0][0];
    dp2[n - 1][m - 1] = mt[n - 1][m - 1];
    for(int i = 1; i < n; i++) {
        dp1[i][0] = dp1[i - 1][0] + mt[i][0];
        dp2[n - i - 1][m - 1] = dp2[n - i][m - 1] + mt[n - i - 1][m - 1];
    }
    for(int j = 1; j < m; j++) {
        dp1[0][j] = dp1[0][j - 1] + mt[0][j];
        dp2[n - 1][m - j - 1] = dp2[n - 1][m - j] + mt[n - 1][m - j - 1];
    }
    for(int i = 1; i < n; i++) {
        for(int j = 1; j < m; j++) {
            dp1[i][j] = max(dp1[i - 1][j], dp1[i][j - 1]) + mt[i][j];
        }
    }
    for(int i = n - 2; i >= 0; i--) {
        for(int j = m - 2; j >= 0; j--) {
            dp2[i][j] = max(dp2[i + 1][j], dp2[i][j + 1]) + mt[i][j];
        }
    }
    vector <pair <int, int>> sums;
    for(int ni = 1; ni < n; ni++) {
        int i = ni, j = 0;
        int mx1 = 0, mx2 = 0;
        while(i >= 0) {
            int cur = dp1[i][j] + dp2[i][j] - mt[i][j];
            if(cur > mx1) {
                mx2 = mx1;
                mx1 = cur;
            } else if(cur > mx2) {
                mx2 = cur;
            }
            i--;
            j++;
        }
        sums.pb({mx2, mx1});
    }
    for(int nj = 1; nj < m - 1; nj++) {
        int j = nj, i = n - 1;
        int mx1 = 0, mx2 = 0;
        while(i >= 0) {
            if(j >= m) break;
            int cur = dp1[i][j] + dp2[i][j] - mt[i][j];
            if(cur > mx1) {
                mx2 = mx1;
                mx1 = cur;
            } else if(cur > mx2) {
                mx2 = cur;
            }
            i--;
            j++;
        }
        sums.pb({mx2, mx1});
    }
    sort(all(sums));
//    for(auto a : sums) cout << a.ff << " " << a.ss << endl;
    cout << sums[0].ff;
}