#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("flip.in");
ofstream fout ("flip.out");
int n,m,s,a,i;
long v[256];
int main()
{
    fin>>n>>m;
    for (i=1;i<=n*m;i++)
        fin>>v[i];

    for (a=1;a<=n*m;a=a+m)
        {
            s=0;
            for (i=a;i<=m+a-1;i++)
                s=s+v[i];
            if (s<-s)
                for (i=a;i<=m+a-1;i++)
                    v[i]=-v[i];
        }

    for (a=1;a<=m;a++)
        {
            s=0;
            for (i=a;i<=n*m;i=i+m)
                s=s+v[i];
            if (s<-s)
                for (i=a;i<=n*m;i=i+m)
                    v[i]=-v[i];
        }
    s=0;
    for (i=1;i<=n*m;i++)
        s=s+v[i];
    fout<<s;
    return 0;
}