#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("flip.in");
ofstream fout("flip.out");

int main(){
    int N, M;   
    fin >> N >> M;

    int tabla[N][M];

    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            fin >> tabla[i][j];

    int j = 1, suma = 0;
    for(int i = 1; i <= N; i ++){
        suma += tabla[i][j];
        if(i == N and suma < 0){
            for(int i = 1; i <= N; i ++) tabla[i][j] *= -1;
            j++;
        }    
    }

    int i = 1;
    suma = 0;
    for(int j = 1; i <= M; j ++){
        suma += tabla[i][j];
        if(j == N and suma < 0){
            for(int j = 1; i <= M; j ++) tabla[i][j] *= -1;
            i++;
        }    
    }

    suma = 0;
    for(int i = 1; i <= N; i++)
        for(int j = 1; j <= M; j++)
            suma += tabla[i][j];

    fout << suma;

    return 0;
}