#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;
    int okP=0;
    for(int i = 0 ; i < N ; i++ )
        for( int j = 0 ; j < M ; j++)
        {
            f>>a[i][j];
            if(a[i][j] <= 0)
                okP=1;

        }

    if(okP == 1)
    {
        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;
}