program area;

var
    done: Boolean;
    i, j: integer;
    data: array[0..99,0..99] of boolean;
    x1, x2, y1, y2: integer;

procedure reportArea;
var
    i, j: integer;
    area: integer;
begin
    area := 0;
    for i:= 0 to 99 do begin
	for j:= 0 to 99 do begin
	    if (data[i,j]) then area := area + 1;
	end;
    end;
    writeln(area:1);
end;

procedure initData;
var
  i, j: integer;
begin
  for i := 0 to 99 do begin
    for j := 0 to 99 do begin
	data[i,j] := false;
    end;
  end;
end;

procedure swap(var i, j: integer);
var
    temp: integer;

begin
    temp:= i;
    i := j;
    j := temp;
    
end;

begin
    done := false;
    initData;
    repeat
	readln(x1, y1, x2, y2);
	if (x1 = -2) then begin
	    reportArea;
	    done := true;
	end else if (x1 = -1) then begin
	    reportArea;
	    initData;
	end else begin
	    if (x2 < x1) then swap(x1, x2);
	    if (y2 < y1) then swap(y1, y2);
	    for i := x1 to (x2-1) do begin
		for j := y1 to (y2-1) do begin
		    data[i,j] := true;
		end;
	    end;
	end;
    until done;
end.