#include <stdio.h>

int main()
{
	FILE *f=fopen("flip.in","r");
	FILE *g=fopen("flip.out","w");
	int n,m,i,j;
	long a[16][16];
	int b;
	long s;

	fscanf(f,"%d %d\n",&n,&m);
	for (i=0; i<n; i++)
	{
		for (j=0; j<m; j++)
			fscanf(f,"%ld",&a[i][j]);
		fscanf(f,"\n");
	}
	do
	{
		b=0;
		for (i=0; i<n; i++)
		{
			s=0;
			for (j=0; j<m; j++)	s+=a[i][j];
			if (s<0)
			{
				for(j=0; j<m; j++)
					a[i][j]=-a[i][j];
				b=1;
			}
		}
		for (j=0; j<m; j++)
		{
			s=0;
			for (i=0; i<n; i++)	s+=a[i][j];
			if (s<0)
			{
				for(i=0; i<n; i++)
					a[i][j]=-a[i][j];
				b=1;
			}
		}
	}
	while (b!=0);
	s=0;
	for (i=0; i<n; i++)
		for (j=0; j<m; j++) s+=a[i][j];
	fprintf(g,"%ld",s);
	fclose(f);
	fclose(g);
	return 0;
}