#include <iostream>
#include <fstream>
using namespace std;

int main()
{
  ifstream input("flip.in");
  int n, m;
  input >> n >> m;
  int a[n][m];
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      input >> a[i][j];
    }
  }

  // Invert negative rows
  for (int i = 0; i < n; i++) {
    long int sum = 0;
    for (int j = 0; j < m; j++) {
      sum += a[i][j];
    }
    if (sum < 0) {
      for (int j = 0; j < m; j++) {
        a[i][j] = 0 - a[i][j];
      }
    }
  }

  // Invert negative columns 
  for (int j = 0; j < m; j++) {
    long int sum = 0;
    for (int i = 0; i < n; i++) {
      sum += a[i][j];
    }
    if (sum < 0) {
      for (int i = 0; i < n; i++) {
        a[i][j] = -a[i][j];
      }
    }
  }

  // Calculate the matrix sum
  long int sum = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      sum += a[i][j];
    }
  }

  ofstream output("flip.out");
  output << sum;
}