What country is the player, with an undisclosed transfer fee and moving to Nacional, from?
CREATE TABLE "players_out" (
  "name" text,
  "country" text,
  "status" text,
  "moving_to" text,
  "transfer_window" text,
  "transfer_fee" text
);
SELECT "country" FROM "players_out" WHERE "transfer_fee"='undisclosed' AND "moving_to"='nacional';