#include <bits/stdc++.h>

using namespace std;
int main(){
    int rows, cols;
    cin >> rows >> cols;

    int sum = 0;
    int last = 0;
    int prelast = 0;
    for(int i = 0; i < rows; i++){
        for(int j = 0; j < cols; j++){
            if(rows % 2 == 0 && cols % 2 == 0){
                if(i == rows - 2 && j == cols-1){
                    cin >> last;
                }
                else if(i == rows-1 && j == cols-1){
                    cin >> prelast;
                }
                else{
                    int x;
                    cin >> x;
                    sum += x;
                }
            }
            else{
                int x;
                cin >> x;
                sum +=x;
            }
        }
    }

    if(last >= prelast){
        sum += last;
    }
    else sum += prelast;

    cout << sum << endl;
}