#include <fstream>
using namespace std;
int a[17][17];
long long s;
short i,j,n,m;
bool sw;
ifstream in("flip.in");
ofstream out("flip.out");
void coloana(short n,short m)
{
    for (i=1;i<=m;i++)
    {s=0;
    for (j=1;j<=n;j++)
    s+=a[j][i];
    if (s<0)
    {
        sw=1;
        for (j=1;j<=n;j++)
        a[j][i]*=-1;
    }
    }
}
void linie(short n,short m)
{
    for (i=1;i<=n;i++)
    {
        s=0;
        for (j=1;j<=m;j++)
        s+=a[i][j];
        if (s<0)
        {
            sw=1;
            for (j=1;j<=n;j++)
            a[i][j]*=-1;
        }
    }
}
void citeste(short n,short m)
{
    for (i=1;i<=n;i++)
    for (j=1;j<=m;j++)
    in>>a[i][j];
}
void suma(short n,short m)
{
    for (i=1;i<=n;i++)
    for (j=1;j<=m;j++)
    s+=a[i][j];
}
int main()
{
    in>>n>>m;
    citeste (n,m);
    do
    {
        sw=0;
        coloana(n,m);
        linie(n,m);
    }
    while(sw==1);
    s=0;
    suma(n,m);
    out<<s<<'\n';
    in.close();
    out.close();
    return 0;
}