#include <fstream>
#define Cmax 16
using namespace std;

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

int main(){
    unsigned short n, m, i, j;
    unsigned C[Cmax][Cmax];
    unsigned long long S;
    fin >> n >> m;
    for (i = 1; i <= n; i++)
    for (j = 1; j <= m; j++)
        fin >> C[n][m];
    for (i = 1; i <= n; i++){
        S = 0;
        for (j = 1; j <= m; j++)
            S += C[i][j];
        if (S < 0)
            for (j = 1; j <= m; j++)
                C[i][j] *= -1;
    }
    S = 0;
    for (i = 1; i <= n; i++)
    for (j = 1; j <= m; j++)
        S += C[i][j];
    fout << S << '\n';
    fin.close();
    fout.close();
    return 0;
}