import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;


public class Main {
    
    public static void main(String[] args) throws FileNotFoundException {
        
        Scanner fisi = new Scanner(new FileInputStream("flip.in"));
        PrintWriter writer = new PrintWriter("flip.out");
        int n, m, sum = 0, suma = 0;
        n = fisi.nextInt();
        m = fisi.nextInt();
        int[][] matrix = new int[n][m];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (fisi.hasNextInt())
                    matrix[i][j] = fisi.nextInt();
            }
        }
        
        
        
        for (int j = 0; j < m; j++) {
            suma = 0;
            for (int i = 0; i < n; i++) {
                suma += matrix[i][j];
            }
            if (suma < 0) {
                for (int i = 0; i < n; i++) {
                    //System.out.println("i = " + matrix[i][j]);
                    matrix[i][j] *= -1;
                }
            }
        }
        
        for (int i = 0; i < n; i++) {
            suma = 0;
            for (int j = 0; j < m; j++) {
                suma += matrix[i][j];
            }
            if (suma < 0) {
                for (int j = 0; j < m; j++) {
                    //System.out.println("j = " + matrix[i][j]);
                    matrix[i][j] *= -1;
                }
            }
        }
        
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                   sum += matrix[i][j];
            }   
        }
        writer.write(String.valueOf(sum));
        writer.close();
        fisi.close();
        
    }
    
}