#include <iostream>
#include <fstream>

using namespace std;

fstream fin("flip.in",ios::in);
fstream fout("flip.out",ios::out);


int main()
{
    int n,m,v[16][16],k,sem1=0,sem2=0;
      fin >> n;
      fin >> m;

//if(n%2!=0) sem1=1;
if(m%2!=0) sem2=1;

    for(int i=1;i<=n;i++)
        for(int j=1; j<=m;j++)
          fin>>v[i][j];


    for(int i=1;i<=n;i++)
     {   k=0;
         for(int j=1; j<=m;j++)

          if(v[i][j]<0) k++; ;

          if(k>=m/2+sem2)  { for(int j=1; j<=m;j++) v[i][j]=(-1)*v[i][j];}
     }

        int s=0;
        for(int i=1;i<=n;i++)

            for(int j=1; j<=m;j++)
             s=s+v[i][j];
        fout<<s;
}