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

int main()
{
    fstream f("flip.in");
    ofstream g("flip.out");

    int N,M,a[16][16];

    f>>N;
    f>>M;
    int sumP, sumN;

    for(int i = 0 ; i < N ; i++ )
        for( int j = 0 ; j < M ; j++)
            f>>a[i][j];

    for(int j = 0 ; j < M ; j++ )
    {
        sumN=0;
        sumP=0;
        for( int i = 0 ; i < N ; i++)
        {
            if(a[i][j] < 0)
            {
                sumN += a[i][j];

            }
            else
            {
                sumP += a[i][j];

            }


        }
        if(sumN * -1 > sumP)
            for( int k = 0 ; k < N ; k++)
                a[k][j] *= -1;
    }

for(int i = 0 ; i < N ; i++ )
    {
        sumN=0;
        sumP=0;
        for( int j = 0 ; j < M ; j++)
        {
            if(a[i][j] < 0)
            {
                sumN += a[i][j];

            }
            else
            {
                sumP += a[i][j];

            }


        }
        if(sumN * -1 > sumP)
            for( int k = 0 ; k < M ; k++)
                a[i][k] *= -1;
    }
    int sum=0;

    for(int i = 0 ; i < N ; i++ )
        for( int j = 0 ; j < M ; j++)
            sum += a[i][j];

    g<<sum;
        return 0;
}