#include<stdio.h>
#include<math.h>
int main()
{
freopen ("flip.in","r",stdin);
freopen("flip.out","w",stdout);
int s=0,i,j,n,m,mat[20][20],gasit=0,gasit1=0;
scanf("%d",&n);
scanf("%d",&m);
for (i=1;i<=n;i++)
	for (j=1;j<=m;j++)
   	scanf("%d",&mat[i][j]);
while(gasit==0 && gasit1==0)
{
gasit=0;
gasit1=0;
for (i=1;i<=n;i++)
	{
   s=0;
	for (j=1;j<=m;j++)
      s+=mat[i][j];
   if (s<0 && mat[i][0]!=-5)
   	{
      mat[i][0]=-5;
      gasit=1;
      for (j=1;j<=m;j++)
      	mat[i][j]=mat[i][j]*(-1);
      }
   }
for (j=1;j<=m;j++)
	{
   s=0;
	for (i=1;i<=n;i++)
   	s+=mat[i][j];
   if (s<0 && mat[i][0]!=-5)
   	{
      mat[0][j]=-5;
      gasit1=1;
      for (i=1;i<=n;i++)
      	mat[i][j]=mat[i][j]*(-1);
      }
   }
 }

s=0;
for (i=1;i<=n;i++)
	for (j=1;j<=m;j++)
   	s+=mat[i][j];
printf("%d",s);
return 0;
}