#include <iostream> 
#include <algorithm>
#include <fstream>

using namespace std ; 

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

int n , m , x , ma1 = 0 , ma2 = 0 ; 

int main(){
    in >> n >> m ; 
    for ( int i = 1 ; i <= n ; i ++ )
    {
        for ( int j = 1 ; j <= m ; j ++ )
        {
            in >> x;
            if ( x < 0 )
            {
                ma1 += x ; 
            }
            else 
            {
                ma2 += x ; 
            }
        }
    }
    ma1 = abs(ma1);
    out << max( ma1 , ma2 );
}