#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;

int main()
{
    ifstream f ("flip.in");
   ofstream g ("flip.out");
   int n,m,i,j,p,neg,a[100][100];
   f>>n>>m;
   for (i=1;i<=n;i++)
    for (j=1;j<=m;j++)
      f>>a[i][j];

   f.close();

   for (j=1;j<=m;j++)
    {  p=0; neg=0;
        for (i=1;i<=n;i++)
      {
          if (a[i][j]>0) p=p+a[i][j];
          else           neg=neg+a[i][j];
      }
      if (neg>p)
      {
          for (i=1;i<=n;i++)
            a[i][j]=a[i][j]*(-1);

      }
    }
   for (i=1;i<=n;i++)
    {  p=0; neg=0;
        for (j=1;j<=m;j++)
      {
          if (a[i][j]>0) p=p+a[i][j];
          else           neg=neg+a[i][j];

      }

      if (neg>p)
      {
          for (j=1;j<=m;j++)
            a[i][j]=(-1)*a[i][j];

      }
    }
    p=0;
   for (i=1;i<=n;i++)
    for (j=1;j<=m;j++)
        p=p+a[i][j];

   g<<p;
   g.close();


    return 0;
}