#include<stdio.h>
#define InFile "filip.in"
#define OutFile "filip.out"
#define Nmax 1000
long  n,m,a[Nmax][Nmax];
void coloana()
{int i,j;
	for(j=1;j<=m;j++)
	{long s=0;
		for(i=1;i<=n;i++)
		   s+=a[i][j];
	if(s<=0) for(i=1;i<=n;i++) a[i][j]*=-1;
	}
}
void suma()
{FILE *fout=freopen(OutFile,"wt",stdout);
long s=0;
coloana();
for(int i=1;i<=n;i++)
 for(int j=1;j<=m;j++) s+=a[i][j];
printf("%ld",s);
fclose(fout);
}
int main()
{int i,j;
	FILE *fin=freopen(InFile,"rt",stdin);
	scanf("%d %d",&n,&m);
	for(i=1;i<=n;i++)
	{long s=0; 
		for(j=1;j<=m;j++)
		{scanf("%ld",&a[i][j]); s+=a[i][j];}
	if(s<=0) for(j=1;j<=m;j++) a[i][j]*=-1;
	}
fclose(fin);
suma();
return 0;
}