#include <fstream>
using namespace std;
ifstream fin("filip.in");
ofstream fout("filip.out");
int sumpoz,sumneg,n,m,i,j,v[25][25],sol;
void read()
{
    fin>>n>>m;
    for (i=1; i<=n; ++i)
        for (j=1; j<=m; ++j)
            fin>>v[i][j];
}
inline void solve()
{
    for (j=1; j<=m; ++j)
    {
        sumneg=sumpoz=0;
        for (i=1; i<=n; ++i)
        {
            if (v[i][j]<0) sumneg += v[i][j]*(-1);
            else if (v[i][j]>0) sumpoz += v[i][j];
        }
        if (sumneg>sumpoz)
        {
            for (i=1; i<=n; ++i)
            {
                v[i][j] *= -1;
            }
        }
    }
    for (i=1; i<=n; ++i)
    {
        sumpoz=sumneg=0;
        for (j=1; j<=m; ++j)
        {
            if (v[i][j]<0) sumneg += v[i][j]*(-1);
            else if (v[i][j]>0) sumpoz += v[i][j];
        }
        if (sumneg>sumpoz)
        {
            for (j=1; j<=m; ++j)
            {
                v[i][j] *= -1;
            }
        }
    }
}
void show()
{
    for (i=1; i<=n; ++i)
    {
        for (j=1; j<=m; ++j)
        {
            sol += v[i][j];
        }
    }
    fout<<sol<<"\n";
}
int main()
{
    read();
    solve();
    show();
    return 0;
}