public class Game {
  // Instance variables to hold the player's gold and inventory
  private int gold;
  private List<String> inventory;

  // Constructor to initialize the game
  public Game() {
    gold = 0;
    inventory = new ArrayList<>();
  }

  // Method to earn gold
  public void earnGold(int amount) {
    gold += amount;
  }

  // Method to buy an upgrade
  public void buyUpgrade(String upgrade) {
    if (gold >= 100) {
      gold -= 100;
      inventory.add(upgrade);
    }
  }

  // Method to buy an invention
  public void buyInvention(String invention) {
    if (gold >= 1000) {
      gold -= 1000;
      inventory.add(invention);
    }
  }

  // Method to get the player's gold
  public int getGold() {
    return gold;
  }

  // Method to get the player's inventory
  public List<String> getInventory() {
    return inventory;
  }

  // Method to upgrade the character
  public void upgradeCharacter(String character) {
    if (inventory.contains("Upgrade")) {
      // Upgrade the character here
    }
  }

  // Main method to run the game
  public static void main(String[] args) {
    Game game = new Game();

    // Earn some gold
    game.earnGold(200);

    // Buy an upgrade
    game.buyUpgrade("Upgrade");

    // Buy an invention
    game.buyInvention("Invention");

    // Upgrade the character
    game.upgradeCharacter("Character");
  }
}