#include <fstream>

int main() {

    std::ifstream in;
    std::ofstream out;
    int n, m, i, j, sum;

    in.open("flip.in");
    if ( in.fail() ) return 1;
    in >> n >> m;
    int a[n][m];
    for ( i = 0; i < n; i++ )
        for ( j = 0; j < m; j++ )
            in >> a[i][j];
    in.close();

    for ( j = 0; j < m; j++ ) {
        sum = 0;
        for ( i = 0; i < n; i++ )
            sum += a[i][j];
        if ( sum < 0 )
            for ( i = 0; i < n; i++ )
                a[i][j] *= -1;
    }

    for ( i = 0; i < n; i++ ) {
        sum = 0;
        for ( j = 0; j < m; j++ )
            sum += a[i][j];
        if ( sum < 0 )
            for ( j = 0; j < m; j++ )
                a[i][j] *= -1;
    }

    sum = 0;
    for ( i = 0; i < n; i++ )
        for ( j = 0; j < m; j++ )
            sum += a[i][j];
    out.open("flip.out");
    if ( out.fail() ) return 1;
    out << sum;
    out.close();

    return 0;
}