#include <fstream.h>

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

int a[16][16], i, j;
long int n, m;
double long sn, sp, s;

int main()
{
 fin >>n >>m;
	for ( i = 0 ; i < n; i ++)
		for ( j = 0 ; j < m; j ++)
			fin >>a[i][j];

	for ( i = 0 ; i < m; i ++)
	{   sp =sn = 0;
		for ( j = 0 ; j < n; j ++)
		   if( a[j][i] > 0)
			sp+=a[j][i];
		   else
			sn+=a[j][i];
		sn*=-1;
		if(sn>sp)
			for( j = 0 ; j <n; j ++)
				a[j][i]*=-1;

	}

	for ( i = 0 ; i < n; i ++)
	{   sp =sn = 0;
		for ( j = 0 ; j < m; j ++)
		   if( a[i][j] > 0)
			sp+=a[i][j];
		   else
			sn+=a[i][j];
		sn*=-1;
		if(sn>sp)
			for( j = 0 ; j <m; j ++)
				a[i][j]*=-1;

	}

	for ( i = 0 ; i < n; i ++)
		for ( j = 0 ; j < m; j ++)
		  s+=a[i][j];


  fout << s;


 fin.close();
 fout.close();
 return 0;
}