#include<iostream>
#include<fstream>

using namespace std;

int main()
{

	int n, m;
	int suma = 0;
	int a[16][16];
	int count = 0;

	ifstream f("flip.in");
	ofstream g("flip.out");

	f >> n >> m;

	for (int i = 1; i <= n;++i)
		for (int j = 1; j <= m; ++j)
			f >> a[i][j];

		for (int j = 1; j <= m; ++j)
		{
			count = 0;
			for (int i = 1; i <= n; ++i)
			{
				if (a[i][j] < 0)
					count++;
			}
			for (int i = 1; i <= n; ++i)
			{
				if (count >n/2)
					suma += -1 * a[i][j];

				else
					suma += a[i][j];
			}
		}
		//for (int i = 1; i <= n; ++i)
		//{
		//	for (int j = 1; j <= m; ++j)
		//		g << a[i][j] << " ";
		//	g << endl;
		//}

		g << suma;

	f.close();
	g.close();

}