#include <iostream>
#include <fstream>

using namespace std;

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

int main()
{
    int a[100][100];
    int m,n,i,j,s;

    //citesc nr de ln si de col
    fin >> m >> n;

    //constructia matricei
    for( i = 0 ; i < m ; i++ )
        for( j = 0 ; j < n ; j++ )
            fin >> a[i][j];

    //comutare pe linii

    j=0;
    s=0;

    while ( j < m )
    {
        for ( i = 0 ; i < n ; i++ )
        s = s + a[j][i];

        if( s < 0 )
            for( i = 0 ; i < n ; i++ )
                a[j][i]=a[j][i]*(-1);

        j=j+1;
        s=0;
    }

    // comutare pe coloane

    s=0;
    j=0;

    while( j < n )
        {
            for ( i = 0 ; i < m ; i++ )
            s = s + a[i][j];

            if( s < 0 )
                for ( i = 0 ; i < m ; i++ )
                    a[i][j]=a[i][j]*(-1);

            j=j+1;
            s=0;

        }

// calculare suma finala
    for ( i = 0 ; i < m ; i++ )
        for ( j = 0 ; j < n ; j++ )
            s+=a[i][j];

    fout<<s;

        return 0;
}