#include<stdio.h>
FILE *in=fopen("flip.in","r"),*out=fopen("flip.out","w");
int n,m,i,j;
long v[16][16],min,max;
int main()
{
fscanf(in,"%d%d",&n,&m);
for (i=1;i<=n;i++)
   for(j=1;j<=m;j++)
      fscanf(in,"%ld",&v[i][j]);
for(i=1;i<=n;i++)
   {
   min=max=0;
   for(j=1;j<=m;j++)
     {
     if(v[i][j]<0)min+=v[i][j];
        else max+=v[i][j];
     }
   if(-min>max)for(j=1;j<=m;j++)v[i][j]=-v[i][j];
   }
for(j=1;j<=m;j++)
   {
   min=max=0;
   for(i=1;i<=n;i++)
     {
     if(v[i][j]<0)min+=v[i][j];
        else max+=v[i][j];
     }
   if(-min>max)for(i=1;i<=n;i++)v[i][j]=-v[i][j];
   }
max=0;
for(i=1;i<=n;i++)
   for(j=1;j<=m;j++)
      max+=v[i][j];
fprintf(out,"%ld",max);
fclose(in);
fclose(out);
return 0;
}