#include<stdio.h>

int main(){
int continuare=1;
long flip[100][100],x,y,i,j,s,st;
FILE *fin=fopen("flip.in","r");
FILE *fout=fopen("flip.out","w");
fscanf(fin,"%ld",&x);
fscanf(fin,"%ld",&y);
s=0;st=0;
while(continuare){
for(i=0;i<y;i++){
 for(j=0;j<x;j++){
  fscanf(fin,"%ld",&flip[j][i]);
  s+=flip[j][i];
 }
if(s<0){
 for(int x1=0;x1<x;x1++)
  flip[x1][i]*=-1;
  continuare=1;
 }
else continuare=0;
  s=0;
}

for(i=0;i<x;i++){
 for(j=0;j<y;j++){
  s+=flip[i][j];
 }

if(s<0){
 for(int x1=0;x1<x;x1++)
  flip[i][x1]*=-1;
continuare=1;
}
else continuare=0;
  s=0;
}
}///big while end
for(i=0;i<y;i++){
 for(j=0;j<x;j++){
 st+=flip[j][i];
 }
}
fprintf(fout,"%ld",st);
fclose(fin);
fclose(fout);
return 0;
}