#include <fstream>
using namespace std;

int main ()
{
	int n, m, s = 0, cont2 = 0, cont1 = 0, c;
	ifstream fin("flip.in");
	ofstream fout("flip.out");
	fin >> n;
	fin >> m;
	cont1 = n;
	cont2 = m;
	while (cont1 <= n)
	{
		while (cont2 <= m)
		{
			fin >> c;
			cont2++;
			if (c >= c * (-1))
				s = s + c;
			else
				s = s + c * (-1);
		}
		cont1++;
	}
	fout << s;
	fin.close();
	fout.close();
	return 0;
}