#include <cstdlib>
#include <fstream>

using namespace std;

int main(void) {

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

    int m, n;
    in >> m >> n;

    int a[n][m];

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            in >> a[i][j];
        }
    }

    for (int i = 0; i < n; i++) {
        int t = 0;
        for (int j = 0; j < m; j++) {
            t += a[i][j];
        }
        if (t < 0) {
            for (int j = 0; j < m; j++) {
                a[i][j] *= -1;
            }
        }
    }

    for (int j = 0; j < m; j++) {
        int t = 0;
        for (int i = 0; i < n; i++) {
            t += a[i][j];
        }
        if (t < 0) {
            for (int i = 0; i < n; i++) {
                a[i][j] *= -1;
            }
        }
    }

    long t = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            t += a[i][j];
        }
    }

    out << t;

    return 0;
}