#include<fstream>
#include<cstdlib>
using namespace std;
int c,i,n,m,s,t;
int main()
{
	ifstream f("flip.in");
	ofstream g("flip.out");
	
	f>>n>>m;

	for(i=1;i<=n*m;i++)
	{
		srand(time(NULL));
		t=rand()%2;
		f>>c;
		
		if(t)
			s+=abs(c);
		else
			s+=c;
	}
	g<<s;
	f.close();
	g.close();
	return 0;
}