//
//  main.cpp
//  Playground
//
//  Created by Andrei-Robert Rusu on 29/05/2020.
//  Copyright © 2020 Andrei-Robert Rusu. All rights reserved.
//

#include <iostream>
#include <fstream>

using namespace std;

fstream fin("flip.in", ios::in);
fstream fout("flip.out", ios::out);

int main(int argc, const char * argv[]) {
    int x,y,i,j, a[16][16];
    
    fin>>x>>y;
    
    for(i = 0; i < x; i++ ) {
      for( j = 0; j < y; j++ ) {
        fin>>a[i][j];
      }
    }
  
    for( i = 0; i < y; i++ ) {
      int t = 0;
      
      for( j = 0; j < x; j++ )
        t += a[i][j];
     
      if( t > 0 )
        continue;
      
      for( j = 0; j < x; j++ )
        a[j][i] *= -1;
    }
    
    for( i = 0; i < x; i++ ) {
      int t = 0;
      
      for( j = 0; j < y; j++ )
        t += a[i][j];
      
      if( t > 0 )
        continue;
      
      for( j = 0; j < y; j++ )
        a[i][j] *= -1;
    }
  
    int sum = 0;
    
    for(i = 0; i < x; i++ ) {
      for( j = 0; j < y; j++ ) {
        sum += a[i][j];
      }
    }
    
    fout<<sum;
    
    return 0;
}