#include<fstream>
using namespace std;

ifstream fin("flip.in");
ofstream fout("flip.out");


int main (){
    
    
    int n , m; 
    fin>>n >>m;
    
    int v[100][101]; 
    
    for ( int i=1 ; i<=n ; i++){
        for ( int j=1 ; j<=m ; j++)
          fin>>v[i][j]; 
    }
    
    
    for ( int i=1 ; i<=n ; i++){
        int a=0 , b=0; 
        for ( int j=1 ; j<=m ; j++){
          if ( v[i][j] > 0 )
            a+=v[i][j]; 
            
         else 
           b+=v[i][j]; 
        }
        
        b = b * -1 ; 
        
        if ( b > a )   { 
            
            for ( int k=1 ; k<=m ; k++){
                v[i][k] = v[i][k] * -1; 
            }
        }
    }
    
    for ( int j=1 ; j<=m ; j++){
        int x = 0 , y = 0 ; 
      for ( int i=1 ; i<=n ; i++){ 
         if ( x > 0 ) x+=v[i][j];
         
         else 
           y+=v[i][j]; 
      }
      
      y = y * -1;
      
      if ( y > x ) { 
      
        for ( int k=1 ; k<=n ; k++)
            v[k][j] = v[k][j] * -1; 
        
      } 
        
           
    } 
     
     int sum = 0; 
      for ( int i=1 ; i<=n ; i++){
        for ( int j=1 ; j<=m ; j++) 
           sum += v[i][j]; 
      }
      
      
         fout<<sum;
    
   
    return 0; 
}