import java.util.ArrayList;
import java.util.HashMap;
import java.util.Scanner;
import java.util.TreeSet;

//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
public class Main {
    static int[]  dp;
    public static void main(String[] args) {
        //TIP Press <shortcut actionId="ShowIntentionActions"/> with your caret at the highlighted text
        // to see how IntelliJ IDEA suggests fixing it.
      Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int c = sc.nextInt();
        long sum = 0;
        long min = Integer.MAX_VALUE;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < c; j++) {
                int l = sc.nextInt();
                sum += l;
                if (min > l && !(( i == 0 && j == 0)
                        || (i == 1 && j == 1)
                        || (i == n - 1 && j == c - 1)
                        || (i == n - 2 && j == c - 2)
                        || (i == n - 2 && j == 0)
                        || (i == n - 1 && j ==1)
                        || (i == 0 && j == c - 2)
                        || (i == 1 && j == c - 1)))  {
                    min = l;
                }
            }
        }
        if (n % 2 == 0 && c % 2 == 0) {
            sum -= min;
        }
        System.out.println(sum );

//
//        String string = sc.next();
//        uuuu(string, "");
//        System.out.println();

    }
//    static TreeSet<String> kombinacie = new TreeSet<>();
//    public static void uuuu(String posibilieties, String current)
//    {
//        if (posibilieties.isEmpty() && !kombinacie.contains(current)) {
//            kombinacie.add(current);
//            return;
//        }
//        for (int i = 0; i < posibilieties.length(); i++) {
//            String ss = posibilieties.charAt(0) + "";
//            current += ss;
//            posibilieties = posibilieties.substring(1);
//            uuuu(posibilieties, current);
//            posibilieties =  posibilieties + current;
//            current = current.substring(0, current.length() - 1);
//        }
//    }

    public static int findThoughtput(int i)
    {
        int [] array = dp;
        int max = Math.min(array[0], array[1]) + Math.min(array[3], array[4]);
        int abrez = Math.max(0, array[1] - array[0]);
        int derez = Math.max(0, array[4] - array[3]);
        int abvolne = Math.max(0, array[0] - array[1]);
        int devolne = Math.max(0, array[3] - array[4]);

        max += Math.max(Math.min(Math.min(abrez, devolne), array[2]), Math.min(Math.min(derez, abvolne), array[2]));

        return max;
    }
}