#include <fstream>

using namespace std;

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


int table[16][16];
int x,y;
bool ChangedLines = true;
bool ChangedColomns = true;

void CheckLines(){
    for(int i = 0;i < x;i++){
        int sum = 0;
        for(int j = 0;j < y;j++){
            sum += table[i][j];
        }
        if(sum < 0){
            for(int j = 0;j < y;j++){
                table[i][j] *= -1;
            }
            ChangedLines = true;
        }
    }
}

void CheckColons(){
    for(int i = 0;i < y;i++){
        int sum = 0;
        for(int j = 0;j < x;j++){
            sum += table[j][i];
        }
        if(sum < 0){
            for(int j = 0;j < x;j++){
                table[j][i] *= -1;
            }
            ChangedColomns = true;
        }
    }
}

int main(){
    in >> x >> y;
    for(int i = 0;i < x;i++)
        for(int j = 0;j < y;j++){
            int a;
            in >> a;
            table[i][j] = a;
        }
    while(ChangedColomns || ChangedLines){
        CheckColons();
        CheckLines();
        ChangedColomns = false;
        ChangedLines = false;
    }
    int sum = 0;
    for(int i = 0;i < x;i++)
        for(int j = 0;j < y;j++)
            sum += table[i][j];
    out << sum;
    return 0;
}