#include<stdio.h>
FILE *f=fopen("flip.in","r"),
     *g=fopen("flip.out","w");
int n,m,a[16][16],i,j,sp,sn,ok;
int main()
{ fsacnf(f,"%d %d",&m,&n);
  for(i=1;i<=m;i++)
    for(j=1;j<=n;j++) fscanf(f,"%d",&a[i][j]);
  while(ok==0){ ok=1;
		for(i=1;i<=m;i++) { sp=0;sn=0;
				    for(j=1;j<=n;j++) if(a[i][j]<0) sn+=a[i][j];
						      else sp+=a[i][j];
				    if(sn*(-1)>sp) ok=0;
				    else for(j=1;j<=n;j++) a[i][j]*=-1;
				  }

		for(i=1;i<=n;i++) { sp=0;sn=0;
				    for(j=1;j<=m;j++) if(a[i][j]<0) sn+=a[i][j]];
						      else sp+=a[i][j];
				    if(sn*(-1)>sp) ok=0;
				    else for(j=1;j<=m;j++) a[i][j]*=-1;
				  }
	       }
  sp=0;
  for(i=1;i<=m;i++) for(j=1;j<=n;j++) sp+=a[i][j];
  fprintf(g,"%d",sp);
  fclose(f);
  fclose(g);
  return 0;
}