#include <fstream>
using namespace std;

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

int main()
{
	int N, M, s = 0, sl = 0, sc = 0;
	fin >> N >> M;
	int a[N][M];
	for(int i = 1; i <= N; i++)
		for(int j = 1; j <= M; j++)
			fin >> a[i][j];
	
	for(int i = 1; i <= N; i++)
	{
		sl = 0;
		sc = 0;
		for(int j = 1; j <= M; j++)
		{
			sl += a[i][j];
			sc += a[j][i];
		}
		if(sl < 0)
			for(int k = 1; k <= M; k++)
				a[i][k] *= -1;
			
		if(sc < 0)
			for(int k = 1; k <= N; k++)
				a[k][i] *= -1;
	}
	
	for(int i = 1; i <= N; i++)
		for(int j = 1; j <= M; j++)
			s += a[i][j];
	fout << s;
	fin.close();
	fout.close();
	return 0;
}