#include <stdio.h>
int main(){
short n,m,i,j,j2;
unsigned long int sp,sn,s;
long int mat[16][16];
FILE *fi,*fo;
fi=fopen("flip.in","rt");
fo=fopen("flip.out","wt");
i=j=j2=1;
sp=sn=s=0;
fscanf(fi,"%d %d",&n,&m);
for (i=1;i<=n;i++){
	for (j=1;j<=m;j++) fscanf(fi,"%d",&mat[i][j]);
}
for (i=1;i<=m;i++){
	for (j=1;j<=n;j++){
	if (mat[i][j]>=0) sp+=mat[i][j];
	else sn+=mat[i][j]*-1;
}
if (sn>sp) {
	for (j2=1;j2<=m;j2++){
	mat[i][j]*=-1;
}}}
sp=sn=0;
for (i=1;i<=n;i++){
	for (j=1;j<=m;j++){
	if (mat[i][j]>=0) sp+=mat[i][j];
	else sn+=mat[i][j]*-1;
}
if (sn>sp) {
	for (j2=1;j2<=m;j2++){
	mat[i][j]*=-1;
}}}
for (i=1;i<=n;i++){
	for (j=1;j<=m;j++) s+=mat[i][j];
}
fprintf(fo,"%d",s);
return 0;
}