#include <iostream>
#include <fstream>
using namespace std;
int mat[16][16];
int main()
{
int n, m, sp, sn, s=0;
ifstream in("flip.in");
ofstream out("flip.out");
in >> n >> m;
for (int i=1;i<=n;++i)
    {
     for (int j=1;j<=m;++j)
        {
         in >> mat[i][j];
        }
    }
for (int i=1;i<=n;++i)
    {
     sp=0;
     sn=0;
     for (int j=1;j<=m;++j)
        {
         if (mat[i][j]>=0)
            {
             sp+=mat[i][j];
            }
            else
                {
                 sn+=mat[i][j];
                }
        }
     if ((-1)*sn>sp)
        {
         for (int j=1;j<=m;++j)
            {
             mat[i][j]*=-1;
            }
        }
    }
for (int i=1;i<=m;++i)
    {
     sp=0;
     sn=0;
     for (int j=1;j<=n;++j)
        {
         if (mat[j][i]>=0)
            {
             sp+=mat[j][i];
            }
            else
                {
                 sn+=mat[j][i];
                }
        }
     if ((-1)*sn>sp)
        {
         for (int j=1;j<=n;++j)
            {
             mat[j][i]*=-1;
            }
        }
    }
for (int i=1;i<=n;++i)
    {
     for (int j=1;j<=m;++j)
        {
         s+=mat[i][j];
        }
    }
out << s;
    return 0;
}