#include<stdio.h>
#include<math.h>

int main(){
long tabla[100][100],n,m,st,sc,max,i,j,x,r,sign;

FILE *fin=fopen("flip.in","r");
FILE *fout=fopen("flip.out","w");

 fscanf(fin,"%ld",&n);
 fscanf(fin,"%ld",&m);
 max=0;sc=0;st=0;r=0;
 sign=1;

for(i=0;i<n;i++){
 for(j=0;j<m;j++){
  fscanf(fin,"%ld",&tabla[i][j]);
 }
}

for(j=0;j<n;j++){
 for(i=0;i<m;i++){
  sc+=abs(tabla[i][j]);
 }
if(max<sc){
max=sc;r=j;}
sc=0;
}

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