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