var mat:array[1..100,1..100] of longint;
    i,j,m,n,sum:longint;

    begin

    assign(input,'flip.in'); reset(input);
    assign(output,'flip.out'); reset(output);
  read(m,n);
    for i:=1 to m do begin
     for j:=1 to n do read(mat[i,j]);
     readln;
     end;

   for i:=1 to m do
    for j:=1 to n do if mat[i,j]<0 then mat[i,j]:=-mat[i,j];

  for i:=1 to m do
   for j:=1 to n do sum:=sum+mat[i,j];
   write(sum);

   close(input);
   close(output);
   end.