#include<fstream.h>

int n, m;
long a[17][17];

void citire()
{
  ifstream in("flip.in");
  in>>n>>m;
  for (int i=1; i<=n; i++)
    for (int j=1; j<=m; j++)
      in>>a[i][j];
  in.close();
}

int prelucrare()
{
  int s, i, j, sm=0;

  for (i=1; i<=n; i++)
    {
      s=0;
      for(j=1; j<=m; j++)
	s+=a[i][j];
      if (s>0) sm+=s;
	else
	  {
	    s=0;
	    for (int k=1; k<=m; k++)
	      {
		a[i][k]*=-1;
		s+=a[i][k];
	      }
	    sm+=s;
	  }
    }
  return sm;
}

int main()
{
  citire();
  int x;
  x=prelucrare();
  ofstream out("flip.out");
  out<<x;
  out.close();
  return 0;
}