#include<stdio.h>

int main(){
long tabla[100][100],n,m,sr,st,sc,i,j,x;
FILE *fin=fopen("flip.in","r");
FILE *fout=fopen("flip.out","w");
fscanf(fin,"%ld",&n);
fscanf(fin,"%ld",&m);
sr=0;sc=0;st=0;
for(i=0;i<n;i++){
 for(j=0;j<m;j++){
  fscanf(fin,"%ld",&tabla[i][j]);
  sr+=tabla[i][j];
 }
 if(sr<0) for(x=0;x<m;x++) tabla[i][x]*=-1;
 sr=0;
}

for(j=0;j<n;j++){
 for(i=0;i<m;i++){
  sc+=tabla[i][j];
 }
if(sc<0) for(x=0;x<n;x++) tabla[x][j]*=-1;
sc=0;
}

for(i=0;i<n;i++){
 for(j=0;j<m;j++){
  st+=tabla[i][j];
 }
}

fprintf(fout,"%ld",st);
fclose(fin);
fclose(fout);

return 0;
}