#include <algorithm>
#include <cassert>
#include <iostream>
#include <vector>

using namespace std;

int main()
{
    std::ios::sync_with_stdio(false);
    std::cin.tie(NULL);
    int maxRow, maxCol;
    cin >> maxRow >> maxCol;

    bool all;
    if(maxRow % 2 == 0 and maxCol % 2 == 0){
        all = false;
    }else all = true;

    int min = 1001;
    long long sum = 0;
    int num;
    bool first = true;
    int diff = maxRow - maxCol;
    for(int row = 0; row < maxRow; ++row)
        for(int col = 0; col < maxCol; ++col){
            cin >> num;
            if(all == true or (row - col) == diff or row == col) sum += num;
            else if(num < min){
                if(first == true) first = false;
                else sum += min;
                min = num;
            }else{
                sum += num;
            }
        }
        

    cout << sum << endl;
}