#include <iostream>
#include <fstream>
using namespace std;

long n;
short m;
long long sum_f = 0;


int main()
{
    ifstream in("flip.in");
    ofstream out("flip.out");
    in >> n >> m;
    long v[n+1][m+1];
    for(long i=1; i<=n; i++)
    {
        long long suma = 0;
        for(int j=1; j<=m; j++)
        {
            in >> v[i][j];
            suma+= v[i][j];
        }
        //cout << suma << endl;
        if(suma < 0)
            for(int j=1; j<=m; j++)
                v[i][j]*=-1;

        if(i==n)
            for(int k=1; k<=m; k++)
            {
                long long suma1 = 0;
                for(long x =1;x<=n;x++)
                    suma1+= v[x][k];
                if(suma1<0)
                    for(long x =1;x<=n;x++)
                        sum_f += v[x][k]*-1;
                else
                    for(long x =1;x<=n;x++)
                        sum_f += v[x][k];
            }

    }
    /*
    for(int i=1;i<=n;i++){
        cout << endl;
        for(int j =1;j<=m;j++)
            cout << v[i][j] << " ";
    } */
    out << sum_f;
    return 0;
}