#include <fstream>

using namespace std;

int main()
{
    ifstream fin("flip.in");
    ofstream fout("flip.out");
    int N, M, i, j, sum=0,psum;
    fin >> N >> M;
    int v[N][M];
    for(i=1;i<=N;++i)
    {
        for (j=1;j<=M;++j)
            fin >> v[i][j];
    }
    i=1;
    while(i<=N){
            psum=0;
          for(j=1;j<=M;++j)
          {
           psum=psum+v[i][j];
          }
          if(psum<psum*(-1))
            {for(j=1;j<=N;++j)
                v[i][j]=v[i][j]*(-1);
            }
            ++i;}
         while(j<=M){
            psum=0;
          for(i=1;i<=N;++i)
          {
           psum=psum+v[i][j];
          }
          if(psum<psum*(-1))
            {for(i=1;i<=N;++i)
                v[i][j]=v[i][j]*(-1);
            }
            ++j;}
            for(i=1;i<=N;++i)
            {
                for(j=1;j<=M;++j)
                    sum=sum+v[i][j];
            }
            fout << sum;
    return 0;
}