#include <fstream>
using namespace std;
ifstream f("flip.in");
ofstream g("flip.out");
int x[21][21], n, m;
void bkt() {
    int s = 0;
    for (int j = 1; j <= m; j++){
        s = 0;
        for (int i = 1; i <= n; i++)
            s = s + x[i][j];
        if (s < 0)
            for (int i = 1; i <= n; i++)
                x[i][j] = x[i][j] * (-1);
    }
    for (int i = 1; i <= m; i++){
        s = 0;
        for (int j = 1; j <= n; j++)
            s = s + x[i][j];
        if (s < 0)
            for (int j = 1; j <= m; j++)
                x[i][j] = x[i][j] * (-1);
    }
    s = 0;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            s = s + x[i][j];
    g << s;
}
int main() {
	f >> n >> m;
	for (int i = 1; i <= n; ++i)
		for (int j = 1; j <= m; ++j)
			f >> x[i][j];
	bkt();
	return 0;
}