# include <fstream>
using namespace std;
int main ()
{
	long N,M,a[100][16],S,S1,S2,i,j;
	ifstream f("flip.in");
	ofstream g("flip.out");
	f>>N>>M;
	for (i=1; i<=N; i++)
		for (j=1; j<=M; j++)
			f>>a[i][j];
	S=0;
	for (i=1; i<=N; i++)
	{
		S1=S2=0;
		for (j=1; j<=M; j++)
		{
			if (a[i][j]<0) S1=S1+a[i][j];
			else S2=S2+a[i][j];
		}
		if (int(S1)>S2) a[i][j]=a[i][j]*(-1);
		S=S+a[i][j];
	}
	g<<S;
	f.close ();
	g.close ();
	return 0;
}