#include <fstream>
using namespace std;

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

int main()
{
	int a[16][16];
	int n, m;
	int sn = 0, sp = 0;
	int st = 0;
	fin >> n >> m;
	
	for ( int i = 0; i < n; i++ )
		for ( int j = 0; j < m; j++ )
			fin >> a[i][j];
	
	for ( int i = 0; i < n; i++ )
	{
		sn = 0;
		sp = 0;
		
		for ( int j = 0; j < m; j++ )
			if ( a[i][j] > 0 )
				sp += a[i][j];
			else
				sn += a[i][j];
		if ( sp < sn )
			for ( int k = 0; k < m; k++ )
			{
				a[i][k] *= -1;
				if ( a[i][k] > 0 )
					st += a[i][k];
			}
		else
			st += sp;
	}
	
	fout << st;
	
	fin.close();
	fout.close();
	return 0;
}