#include <fstream>
using namespace std;
ifstream cin("flip.in");
ofstream cout("flip.out");
int n, m, i, j, a[20][20];
long long s;
int main()
{
    cin>>n>>m;
    for(i=1;i<=n;++i)
        for(j=1;j<=m;++j)
            cin>>a[i][j];
    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]=-a[i][j];
    }
    for(i=1;i<=m;++i)
    {
        s=0;
        for(j=1;j<=n;++j)
            s+=a[i][j];
        if(s<0)
            for(j=1;j<=m;++j)
                a[i][j]=-a[i][j];
    }
    s=0;
    for(i=1;i<=n;++i)
        for(j=1;j<=m;++j)
            s+=a[i][j];
    cout<<s;
    return 0;
}