var
	a:array[1..16,1..16] of longint;
	n,m,i,j:integer;
	suma:longint;
	
procedure change_c(col:integer);
	var
		ii:integer;
	begin
		for ii:=1 to n do
			a[ii,col]:=a[ii,col]*(-1);
	end;
	
procedure coloana;
	var
		neg,poz:longint;
	begin
		for i:=1 to m do begin
			poz:=0;
			neg:=0;
			for j:=1 to n do begin
				if a[j,i] > 0 then poz:=poz+a[j,i] else neg:=neg+a[j,i];
				if neg*(-1) > poz then change_c(i);
			end;
		end;
	end;
	
procedure change_l(lin:integer);
	var
		ii:integer;
	begin
		for ii:=1 to m do
			a[lin,ii]:=a[lin,ii]*(-1);
	end;
	
procedure linie;
	var
		neg,poz:longint;
	begin
		for i:=1 to n do begin
			poz:=0;
			neg:=0;
			for j:=1 to n do begin
				if a[i,j] > 0 then poz:=poz+a[i,j] else neg:=neg+a[i,j];
				if neg*(-1) > poz then change_l(i);
			end;
		end;
	end;
	
begin
	assign(input,'flip.in');reset(input);
	assign(output,'flip.out');rewrite(output);
	readln(n,m);
	for i:=1 to n do
		for j:=1 to m do
			read(a[i,j]);
	coloana;
	linie;
	suma:=0;
	for i:=1 to n do
		for j:=1 to m do
			suma:=a[i,j]+suma;
	writeln(suma);
end.