#include<fstream.h>

ifstream fin("flip.in");
ofstream fout("flip.out");

int a[17][17];
int i, n, m, j;

int main()
{
    fin>>n>>m;
    for(i = 1;i<=n;i++)
          for(j = 1;j<=m;j++)
                fin>>a[i][j];
    fin.close();
    int gata = 0, sumap, suman;
    while(gata == 0)
    {
               suman = 0;
               sumap = 0;
               gata = 1;
               for(i = 1;i<=n;i++)
               {
                     for(j = 1;j<=m;j++)
                           if( a[i][j] < 0) suman = suman + a[i][j];
                           else             sumap = sumap + a[i][j];
                     if(sumap < suman)
                     {
                              for(j = 1;j<=m;j++)
                                    a[i][j] = a[i][j] * -1;
                              gata = 0;
                     }
               }
    }
    int suma = 0;
    for(i = 1;i<=n;i++)
          for(j = 1;j<=m;j++)
                suma = suma + a[i][j];
    fout<<suma;
    fout.close();
    return 0;
}