#include <fstream>

using namespace std;

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

int n, m, i, j, a[16][16], v[16], w[16], suma, maxim;
bool orizontal = true, vertical = true;

int main()
{
    fin >> n >> m;

    for(i = 1; i <= n; i++){
        for(j = 1; j <= m; j++){
            fin >> a[i][j];
        }
    }
    if(n > m){ maxim = n;}
    else {maxim = m;}

    while((orizontal == true) || (vertical == true)){
        for(i = 1; i <= 2*maxim; i++){
            v[i] = 0;
            w[i] = 0;
        }

        for(i = 1; i <= n; i++){
            for(j = 1; j <= m; j++){
                v[i] = v[i] + a[i][j];
            }
        }
        orizontal = false;

        for(i = 1; i <= n; i++){
            if(v[i] < 0){
                for(j = 1; j <= m; j++){
                    a[i][j] = (-1) * a[i][j];
                }
                orizontal = true;
            } else {
                // nothing
            }
        }

        for(i = 1; i <= n; i++){
            for(j = 1; j <= m; j++){
                w[j] = w[j] + a[i][j];
            }
        }
        vertical = false;

        for(j = 1; j <= m; j++){
            if(w[j] < 0){
                for(i = 1; i <= n; i++){
                    a[i][j] = (-1) * a[i][j];
                }
                vertical = true;
            } else {
                // nothing
            }
        }
    }

    for(i = 1; i <= n; i++){
        for(j = 1; j <= m; j++){
            suma = suma + a[i][j];
        }
    }

    fout << suma;

    return 0;
}