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


int main(){

    int N, M;

    std::cin >> N >> M;

    int minimum = INT32_MAX;
    long long  sum;
    std::cin >> sum;
    



    for(int i = 1; i < N * M - 1; i++){
        int value;
        std::cin >> value;
        sum += value;
        if(i % 2 == 1){
            minimum = std::min(minimum, value);
        }

    }

    int end;
    std::cin >> end;
    sum += end;

    //std::cout << "sum: " << sum << std::endl;
    //std::cout << "minimum: " << minimum << std::endl;

    if(N % 2 == 1 || M % 2 == 1){
        std::cout << sum;
    }
    else{
        std::cout << sum - minimum;
    }

    return 0;
}