#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define int long long
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()

int n, m;
vector<int> a;

void solve() {

}

signed main() {
    cin >> n >> m;
    int a[n][m];
    for (int i=0; i<n; i++)
        for (int j=0; j<m; j++)
            cin >> a[i][j];
    
    int sum = 0;
    for (int i=0; i<n; i++)
        for (int j=0; j<m; j++)
            sum += a[i][j];
    
    vector<pair<int, int>> b{{0, 0}, {1, 1}, {0, m - 2}, {1, m - 1}, {n - 2, 0}, {n - 1, 1}, {n - 2, m - 2}, {n - 1, m - 1}};
    if (n % 2 || m % 2)
    {
        cout << sum << endl;
        return 0;
    }
    else {
        int mn = INT32_MAX;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                pair<int, int> idx{i, j};
                bool F = 1;
                for (auto cant : b) {
                    if (cant == idx) F = 0;
                }
                if (F) mn = min(mn, a[i][j]);
            }
        }
        cout << sum - mn << endl;
    }

    solve();
    return 0;
}