#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
int main()
{
  int i, j, m, n, a[16][16], neg, poz, s = 0;
  ifstream f("flip.in");
  ofstream g("flip.out");
  f >> m >> n;
  for (i = 1; i <= m; i++)
    for (j = 1; j <= n; j++)
      f >> a[i][j];
  for (i = 1; i <= m; i++) {
    neg = 0; poz = 0;
    for (j = 1; j <= n; j++)
      if (a[i][j] < 0) neg += a[i][j];
      else poz += a[i][j];
    if (abs(neg) > abs(poz)) 
      for (j = 1; j <= n; j++)
        a[i][j] *= -1;
  }
  for (i = 1; i <= n; i++) {
    neg = 0; poz = 0;
    for (j = 1; j <= m; j++)
      if (a[i][j] < 0) neg += a[i][j];
      else poz += a[i][j];
    if (abs(neg) > abs(poz)) 
      for (j = 1; j <= m; j++)
        a[i][j] *= -1;
  }
  for (i = 1; i <= m; i++)
    for (j = 1; j <= n; j++)
      s += a[i][j];
  g << s;
  f.close();
  g.close();
  return 0;
}