#include <bits/stdc++.h>

using namespace std;

using ll = long long;
#define dbl long double
#define vec vector
#define um unordered_map
#define us unordered_set

using ull = unsigned long long;
using vi = vec<int>;
using vl = vector<ll>;
using vd = vector<double>;
using pii = pair<int,int>;
using pll = pair<ll, ll>;
using pdd = pair<dbl, dbl>;

int main(){
    cin.sync_with_stdio(false);
    cin.tie(0);
    cin.exceptions(ios::failbit);
    int r, c;
    cin >> r >> c;
    if (r % 2 != 0 || r % 2 != 0) {
        ll acc = 0;
        for (int i = 0; i < r; i++) {
            for (int j = 0; j < c; j++) {
                int x;
                cin >> x;
                acc += x;
            }
        }
        cout << acc << endl;
        return 0;
    }
    ll min1 = 1e6;
    ll acc = 0;
    for (int i = 0; i < r; i++) {
        for (int j = 0; j < c; j++) {
            int x;
            cin >> x;
            acc += x;
            if ((i == 0 && j == 0) || (i == r - 1 && j == c - 1)) {
                continue;
            }
            if (x < min1) min1 = x;
        }
    }
    cout << acc - min1 << endl;
}