contract MyAdvancedToken is token {

  uint256 public sellPrice;
  uint256 public buyPrice;

  mapping (address => bool) public frozenAccount;

  /* This generates a public event on the blockchain that will notify clients */
  event FrozenFunds(address target, bool frozen);

  /* Initializes contract with initial supply tokens to the creator of the contract */
  function MyAdvancedToken(
      uint256 initialSupply,
      string tokenName,
      uint8 decimalUnits,
      string tokenSymbol
  ) token (initialSupply, tokenName, decimalUnits, tokenSymbol) {}

  /* Internal transfer, only can be called by this contract */
  function _transfer(address _from, address _to, uint _value) internal {
      require (_to != 0x0);                               // Prevent transfer to 0x0 address. Use burn() instead
      require (balanceOf[_from] > _value);                // Check if the sender has enough
      require (balanceOf[_to] + _value > balanceOf[_to]); // Check for overflows
      require(!frozenAccount[_from]);                     // Check if sender is frozen
      require(!frozenAccount[_to]);                       // Check if recipient is frozen
      balanceOf[_from] -= _value;                         // Subtract from the sender
      balanceOf[_to] += _value;                           // Add the same to the recipient
      Transfer(_from, _to, _value);
  }

  /// @notice Create `mintedAmount` tokens and send it to `target`
  /// @param target Address to receive the tokens
  /// @param mintedAmount the amount of tokens it will receive
  function mintToken(address target, uint256 mintedAmount) onlyOwner {
      balanceOf[target] += mintedAmount;
      totalSupply += mintedAmount;
      Transfer(0, this, mintedAmount);
      Transfer(this, target, mintedAmount);
  }

  /// @notice `freeze? Prevent | Allow` `target` from sending & receiving tokens
  /// @param target Address to be frozen
  /// @param freeze either to freeze it or not
  function freezeAccount(address target, bool freeze) onlyOwner {
      frozenAccount[target] = freeze;
      FrozenFunds(target, freeze);
  }

  /// @notice Allow users to buy tokens for `newBuyPrice` eth and sell tokens for `newSellPrice` eth
  /// @param newSellPrice Price the users can sell to the contract
  /// @param newBuyPrice Price users can buy from the contract
  function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner {
      sellPrice = newSellPrice;
      buyPrice = newBuyPrice;
  }

  /// @notice Buy tokens from contract by sending ether
  function buy() payable {
      uint amount = msg.value / buyPrice;               // calculates the amount
      _transfer(this, msg.sender, amount);              // makes the transfers
  }

  /// @notice Sell `amount` tokens to contract
  /// @param amount amount of tokens to be sold
  function sell(uint256 amount) {
      require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
      _transfer(msg.sender, this, amount);              // makes the transfers
      msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
  }
}
function sell(uint256 amount) {
    require(this.balance >= amount * sellPrice);      // checks if the contract has enough ether to buy
    _transfer(msg.sender, this, amount);              // makes the transfers
    msg.sender.transfer(amount * sellPrice);          // sends ether to the seller. It's important to do this last to avoid recursion attacks
}

/// @notice Sell `amount` tokens to contract
/// @param amount amount of tokens to be sold