import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner in = new Scanner(System.in);

        int row = in.nextInt();
        int col = in.nextInt();

        int min = 1001;
        int sum = 0;

        if (row % 2 == 0 && col % 2 == 0) {
            for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                    int c = in.nextInt();

                    if (i + j % 2 == 1) {
                        min = Math.min(min, c);
                    }

                    sum += c;
                }
            }

            sum -= min;
        } else {
            for (int i = 0; i < row * col; i++) {
                sum += in.nextInt();
            }
        }

        System.out.println(sum);
    }
}