#include<fstream>
using namespace std;
ifstream fin("flip.in");
ofstream fout("flip.out");

int main()
{
	int m , n , a[100][100],i,j,s,sn,sp;
	fin >> n >> m;
	for( i = 1; i <= n; i++ )
		for( j = 1; j <= m; j++ )
			fin >> a[i][j];
		
	for( i = 1; i <= n; i++ )
	{
		sp = 0;
		sn = 0;
		for( j = 1; j <= m; j++ )
		{	if( a[i][j] < 0 )sn = sn + a[i][j];
			if( a[i][j] > 0 )sp = sp + a[i][j];
		}
		//fout << sn << " "<<sp <<'\n';
		if( (-1)*sn > sp )
		{	
			for( j = 1; j <= m;j++ )
				a[i][j]= (-1)*a[i][j];
		}
	}
	
	
	
	for( j = 1; j <= m; j++)
	{
		sn=0;
		sp=0;
		for( i = 1; i <= n; i++ )
			{	if( a[i][j] < 0 )sn = sn + a[i][j];
				if( a[i][j] > 0 )sp = sp + a[i][j];
			}
			//fout << sn << " "<<sp <<'\n';
			if( (-1)*sn > sp )
			{	
			for( i = 1; i <= n;i++ )
				a[i][j]= (-1)*a[i][j];
			}
	}
	s= 0;
	for( i = 1; i <= n; i++ )
	
		for( j = 1; j <= m; j++ )
			s = s + a[i][j];
			fout << s;
			
	/*for( i = 1; i <= n; i++ )
		{
			fout << '\n';
			for( j = 1; j <= m; j++ )
			fout << a[i][j]<<" ";			
		}*/
fin.close();
fout.close();
return 0;
}