#include <fstream>
#include <vector>

using std::vector; using std::ifstream;
using std::ofstream;

//avem o matrice de cel mult 16x16
//putem inversa fie linii fie coloane
//vom avea 32 tipuri de operatii:
//l1,l2,...,l16
//c1,c2,...,c16
//unde: lX -> inverseaza linia X; cX -> inverseaza coloana X
//la inceput, fiecare operatie are un avantaj/dezavantaj
//executarea operatiilor: l2,c3 schimba avantajul operatiei c3
//executarea operatiilor: c2,c3 NU schimba avantajul operatiei c3
//executarea operatiilor c2,c3 este acelasi lucru cu executarea operatiilor c3,c2
//formam toate posibilitatile de a inversa coloanele:
//De cate o op: {c1} {c2} ... {c16} (16 posibilitati)
//De cate 2 op: {c1,c2} {c2,c3} ... {c15,c16} (15 posibilitati)
//De cate 3 op: {c1,c2,c3} {c2,c3,c4} {c3,c4,c5} {c4,c5,c6} {c5,c6,c7}
//              {c6,c7,c8} {c7,c8,c9} {c8,c9,c10} {c9,c10,c11} {c10,c11,c12}
//              {c11,c12,c13} {c12,c13,c14} {c13,c14,c15} {c14,c15,c16} (14 posibilitati)
//...
//Deci avem: 16+15+14+13+...+1 posibilitati, adica 16*17/2 = 136 posibilitati
//pentru fiecare posibilitate o sa iei doar operatiile linilor care sunt in avantaj

//putem nota o operatie numeric
//astfel, c(1..16) vor avea valorile 1..16 si l(1..16) vor avea valorile 17..33

const unsigned int MAX_OP = 32;
const unsigned int MAX_MAT_SIZE = 16;

struct Mat {
	long mat[MAX_MAT_SIZE][MAX_MAT_SIZE];
	unsigned int nr_l,nr_c;
};

/*
inline char c(unsigned int i){return char(i%MAX_MAT_SIZE);}
inline char l(unsigned int i){return char(i%MAX_MAT_SIZE+MAX_MAT_SIZE);}
*/

//inverseaza coloanele [start_col;end_col) din matricea in si obtine noua matrice out
void matinvcols (const Mat &in, unsigned int start_col,
					unsigned int end_col, Mat &out)
{
	for (unsigned int col=0; col<in.nr_c; col++) {
		for (unsigned int line=0; line<in.nr_l; line++) {
			if (col>=start_col && col<end_col)
				out.mat[line][col] = -in.mat[line][col];
			else
				out.mat[line][col] = in.mat[line][col];
		}
	}
	out.nr_l = in.nr_l;
	out.nr_c = in.nr_c;
}

long sum (const Mat &mat) {
	long ret=0;
	for (unsigned int i=0; i<mat.nr_l; i++)
        for (unsigned int j=0; j<mat.nr_c; j++)
            ret += mat.mat[i][j];
	return ret;
}

int main (void)
{
    Mat mat,mat2;
    
	ifstream f_in("flip.in");
    ofstream f_out("flip.out");
    
	f_in>>mat.nr_l>>mat.nr_c;
    for (unsigned int i=0; i<mat.nr_l; i++)
        for (unsigned int j=0; j<mat.nr_c; j++)
            f_in >> mat.mat[i][j];
    f_in.close();
	
	/*vector<char> op(MAX_OP), bestop(MAX_OP);*/
	long max_sum = sum(mat);
	//din cate operatii sa fie formata solutia: [1;16]
	for (unsigned int nr_op=1; nr_op<=16; nr_op++) {
		//de la a cata operatie sa inceapa: [0;15-nr_op+1]
		for (unsigned int offset=0; offset<=16-nr_op; offset++) {
			//avem solutia [offset;offset+nr_op)
			/*op.erase();
			for (unsigned int i=0; i<nr_op; i++)
				op.push_back( c(offset+i) );*/

			matinvcols(mat, offset, offset+nr_op, mat2);

			//cautam toate liniile in dezavantaj, le inversam
			for (unsigned int lin=0; lin<mat2.nr_l; lin++) {
				long lin_sum=0;
				for (unsigned int col=0; col<mat2.nr_c; col++)
					lin_sum += mat2.mat[lin][col];
				if (lin_sum < 0) {
					/*op.push_back( l(lin) );*/
					//inversam linia lin, adica executam operatia l(lin)
					for (unsigned int col=0; col<mat2.nr_c; col++)
						mat2.mat[lin][col] *= -1;
				}
			}
			//calculam suma matricii dupa operatii
			long sum_this = sum(mat2);
			if (sum_this > max_sum) {
				// am obtinut un nou maxim
				max_sum = sum_this;
//				bestop = op;
			}
		}
	}
	f_out << max_sum << '\n';
    f_out.close();
    return 0;
}