#include <iostream>

int main() {
    int lines, columns;
    std::cin >> lines;
    std::cin >> columns;

    bool twoEvens = ((lines % 2 == 0) && (columns % 2 == 0));

    long long sum = 0;
    long long min = -1;
    for (int i = 0; i < lines; i++) {
        for (int j = 0; j < columns; j++) {
            long long currentNum;
            std::cin >> currentNum;
            sum = sum + currentNum;
            bool isStart = ((i == 0) && (j == 0));
            bool isEnd = ((i == lines - 1) && (j == columns - 1));
            if ((!isStart) && (!isEnd) && ((min == -1) || (min > currentNum))) {
                min = currentNum;
            }
        }
    }

    std::cout << sum - (twoEvens ? min : 0);

    return 0;
}