#include <fstream>
#define NMax 20

using namespace std;

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

int M[NMax][NMax];

int main()
{
    int n, m, i, j, ok = 1, sum;

    in >> n >> m;

    for(i = 1; i <=n; i ++)
        for(j = 1; j <= m; j ++)
            in>>M[i][j];
    while(ok)
    {
        ok = 0;
        for(i = 1; i <= m; i ++)
        {
            sum = 0;
            for(j = 1; j <= n; j ++)
                sum += M[j][i];
            if(sum < 0)
            {
                for(j = 1; j <= n; j ++)
                    M[j][i] = M[j][i] * (-1);
                ok = 1;
            }
        }

        for(i = 1; i <= n; i ++)
        {
            sum = 0;
            for(j = 1; j <= m; j ++)
                sum += M[i][j];
            if(sum < 0)
            {
                for(j = 1; j <= m; j ++)
                    M[i][j] = M[i][j] * (-1);
                ok = 1;
            }
        }
    }

    sum = 0;
    for(i = 1; i <= n; i ++)
        for(j = 1; j <= m; j ++)
            sum += M[i][j];
    out << sum;

    return 0;
}