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

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

int coltot[16];
int matrix[16][16];
int main()
{
    int n, m, total = 0;
    fin >> n >> m;
    //cin >> n >> m;
    for(int i = 0; i < n; i ++)
    {
        for(int j = 0; j < m; j ++)
        {
            //cin >> matrix[i][j];
            fin >> matrix[i][j];
            coltot[j] += matrix[i][j];
            total += matrix[i][j];
        }
        if(total < 0)
        {
            for(int j = 0; j < m; j ++)
            {
                matrix[i][j] = matrix[i][j] * -1;
            }
        }
        total = 0;
    }
    for(int i = 0; i < m; i ++)
    {
        if(coltot[i] < 0)
        {
            for(int j = 0; j < n; j ++)
            {
                matrix[j][i] = matrix[j][i] * -1;
            }
        }
    }
    total = 0;
    for(int i = 0; i < n; i ++)
    {
        for(int j = 0; j < m; j ++)
        {
            total += matrix[i][j];
        }
    }
    fout << total << endl;
    //cout << total;
}