#include <fstream>

using namespace std;

int main()
{
	ifstream IN("flip.in");
	ofstream OUT("flip.out");

	int lines, columns, table[17][17];
	int sumTotal = 0 ;
	int sum;

	IN >> lines >> columns;

	for (int i = 0 ; i < lines ; i++)
	{
		for (int j = 0 ; j < columns ; j++)
		{
			IN >> table[i][j];
		}
	}

	for ( int i = 0 ; i < lines; i++)
	{
		sum = 0 ;

		for (int j = 0 ; j < columns ; j++)
		{
			sum += table[i][j];
		}

		if (sum < 0) 
		{
			OUT << "line: " << i << "\n";

			for (int j = 0 ; j < columns ; j++)
			{
				table[i][j] = -table[i][j];

				
			}
		}
	}

	for (int i = 0 ; i < columns ; i++)
	{
		sum = 0;

		for (int j = 0 ; j < lines ; j++)
		{
			sum += table[j][i];
		}

		if (sum < 0) 
		{
			OUT << "column: " << i << "\n";

			for (int j = 0 ; j < lines ; j++)
			{
				table[j][i] = -table[j][i];
				
				
			}
		}
	}

	for (int i = 0 ; i < lines; i++)
		for (int j = 0 ; j < columns ; j++)
			sumTotal += table[i][j];

	OUT << sumTotal << "\n";

}