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

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<pair<int, int>> vpii;

template<class T> using vec = vector<T>;
template<class T> using uset = unordered_set<T>;
template<class K, class V> using umap = unordered_map<K, V>;

void solve () {
    ll N, M;

    cin >> N >> M;

    vvi larvea = vvi(N, vi(M));

    ll sum = 0;

    rep(i, 0, N) {
        rep(i2, 0, M) {
            int count;
            cin >> count;

            larvea[i][i2] = count;
            sum += count;
        }
    }

    if (N % 2 || M % 2) {
        cout << sum << endl;
    }
    else {
        cout << sum - min(larvea[N-1][M-2], larvea[N-2][M-1]) << endl;
    }
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit);

    ll T = 1;
    //cin >> T;
    rep(i, 0, T) solve();

    return 0;
}