// flip.cpp : Defines the entry point for the console application.
//

#include <stdio.h>
int e[257];
int main()
{
	int m,n,i,suma=0,j;
	FILE *f1,*f2;
	f1=fopen("flip.in","r");
	f2=fopen("flip.out","w");
	fscanf(f1,"%d %d",&n,&m);
	for(i=1;i<=n*m;i++)
		fscanf(f1,"%d",&e[i]);
	for(i=1;i<=n*m;i=i+m)
	{
		suma=0;
		for(j=i;j<m+i;j++)
			suma=suma+e[j];
		if(suma<0)
			for(j=i;j<m+i;j++)
				e[j]=-e[j];
	}
	for(i=m;i>0;i--)
	{
		suma=0;
		for(j=i;j<=n*m;j=j+m)
			suma=suma+e[j];
		if(suma<0)
			for(j=i;j<=n*m;j=j+m)
				e[j]=-e[j];
	}
	suma=0;
	for(i=1;i<=n*m;i++)
		suma=suma+e[i];
	fprintf(f2,"%d",suma);
	fclose(f1);
	fclose(f2);

	return 0;
}