#include<fstream>
using namespace std;


int main(){
	int n, m, a[16][16], i, ii, jj, j, s1, s2, stotal = 0;
	ifstream f("flip.in");
	ofstream g("flip.out");

	f>>n>>m;
	
	for(i = 0; i < n; i++)
		for(j = 0; j < m; j++)
			f>>a[i][j];	

	for(i = 0; i < n; i++){		
		for(j = 0; j < m; j++){
			if (a[i][j] < 0){
				s1 = 0;
				s2 = 0;
				for(ii = 0; ii < n; ii++){					
						if(a[ii][j] < 0)
							s1 += a[ii][j];
						else
							s2 += a[ii][j];
				}
				if (abs(s1) > s2)
					for(ii = 0; ii < n; ii++)
						a[ii][j] *= -1;
				
			}
		}
	}

	for(j = 0; j < m; j++){		
		for(i = 0; i < n; i++){
			if (a[i][j] < 0){
				s1 = 0;
				s2 = 0;
				for(jj = 0; jj < m; jj++){					
					if(a[ii][j] < 0)
						s1 += a[i][jj];
					else
						s2 += a[i][jj];
				}
				if (abs(s1) > s2)
					for(jj = 0; jj < m; jj++)
						a[i][jj] *= -1;

			}
		}
	}

	for(i = 0; i < n; i++)
		for(j = 0; j < m; j++)
			stotal += a[i][j];

	g<<stotal;
	

	f.close();
	g.close();
	return 0;

}