#include<stdio.h>
FILE *in=fopen("flip.in","r");
FILE *out=fopen("flip.out","w");
long a[20][20],i,s,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=0;
		for(j=1;j<=m;j++)
			s+=a[i][j];
		if(s<0)
			for(j=1;j<=m;j++) a[i][j]*=-1;
	}
	for(i=1;i<=n;i++)
	{
		s=0;
		for(j=1;j<=m;j++)
			s+=a[j][i];
		if(s<0)
			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;
}