program flip;

var
   n, m, i, j, k, sum: longint;
   f: text;

begin
   assign(F, 'flip.in');
   sum:=0;
   reset(F);
   readln(f, N, M);
   for i:= 1 to n do
      begin
         for j:= 1 to m do
            begin
               read(f, k);
               sum:=sum+abs(k);
            end;
         readln(F);
      end;
   close(F);
   assign(f, 'flip.out');
   rewrite(F);
   writeln(f, sum);
   close(F);
end.