#include <bits/stdc++.h>

using namespace std;

int main(int argc, char* argv[])
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    uint64_t tt = 1; /* cin >> tt; */
    while(tt--)
    {
        uint64_t n, m; cin >> n >> m;
        uint64_t res = 0;

        vector<vector<uint64_t>> v;
        for(uint64_t i = 0; i < n; i++)
        {
            vector<uint64_t> vv;
            for(uint64_t ii = 0; ii < m; ii++)
            {
                uint64_t x; cin >> x;
                res += x;
                vv.push_back(x);
            }
            v.push_back(vv);
        }

        if(n % 2 == 0 && m % 2 == 0)
        {
            res -= min(v[n - 1][m - 2], v[n - 2][m - 1]);
        }

        cout << res << "\n";
    }

    return 0;
}