#include<fstream>
using namespace std;
int main()
{
    ifstream fin("flip.in");
    ofstream fout("flip.out");
    int n,m;
    fin>>n>>m;
    int a[17][17];
    
    int i,j,s;
    
    for(i=1;i<=n;i++){
                      for(j=1;j<=m;j++){fin>>a[i][j];}
                      }
    
    //coloane
    for(j=1;j<=m;j++){
                      s=0;
                      for(i=1;i<=n;i++){s+=a[i][j];}
                      if(s<0){
                              for(i=1;i<=n;i++){a[i][j]*=-1;}
                              }
                      }
    
    //linii
    for(i=1;i<=n;i++){
                      s=0;
                      for(j=1;j<=m;j++){s+=a[i][j];}
                      if(s<0){
                              for(j=1;j<=m;j++){a[i][j]*=-1;}
                              }
                      }
    
    //suma 
    s=0;
    for(i=1;i<=n;i++){
                      for(j=1;j<=m;j++){s+=a[i][j];}
                      }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}