#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>

using namespace std;

int main(){

    int N, M;
    cin >> N >> M;
    int minimum = INT32_MAX;
    int sum = 0;

    for (int i = 0; i < N; i++){
        for(int j = 0; j < M; j++){

            int a;
            cin >> a;
            sum += a;

            if((i == 0 && j == 0) 
             || (i == N-1 && j == M-1)
             || (i == j)
             || (i + (M-N) == j)    
            ){
                continue;
            } else{
                minimum = min(minimum, a);
            }
        }
    }

    //cout << "sum: " << sum << ", min: " << minimum << endl; 

    if (N % 2 == 0 && M % 2 == 0){
        sum -= minimum;
    }

    cout << sum << endl;

    return 0;
}