#include<stdio.h>
FILE *in=fopen("flip.in","r");
FILE *out=fopen("flip.out","w");
long a[20][20],i,s,s_neg,s_poz,j;
int n,m;
int main()
{
	fscanf(in,"%d%d",&n,&m);
	for(i=1;i<=n;i++) 
		for(j=1;j<=m;j++)
			fscanf(in,"%ld",&a[i][j]);
	for(i=1;i<=n;i++)
	{
		s_neg=s_poz=0;
		for(j=1;j<=m;j++)
			if(a[i][j]<0) s_neg+=(a[i][j]*(-1));
			else s_poz+=a[i][j];
		if(s_neg>s_poz)
			for(j=1;j<=m;j++) a[i][j]*=-1;
	}
	for(i=1;i<=n;i++)
	{
		s_neg=s_poz=0;
		for(j=1;j<=m;j++)
			if(a[j][i]<0) s_neg+=(a[j][i]*(-1));
			else s_poz+=a[j][i];
		if(s_neg>s_poz)
			for(j=1;j<=m;j++) a[j][i]*=-1;
	}
	for(i=1;i<=n;i++) 
		for(j=1;j<=m;j++)
			if(a[i][j]>0) s+=a[i][j];
	fprintf(out,"%ld",s);
	return 0;
}