pragma solidity 0.4.24;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

  contract ERC20 {
  function totalSupply()public view returns (uint total_Supply);
  function balanceOf(address _owner)public view returns (uint256 balance);
  function allowance(address _owner, address _spender)public view returns (uint remaining);
  function transferFrom(address _from, address _to, uint _amount)public returns (bool ok);
  function approve(address _spender, uint _amount)public returns (bool ok);
  function transfer(address _to, uint _amount)public returns (bool ok);
  event Transfer(address indexed _from, address indexed _to, uint _amount);
  event Approval(address indexed _owner, address indexed _spender, uint _amount);
}


contract HongKongMonetaryAuthority is ERC20
{using SafeMath for uint256;
   string public constant symbol = ",000.HKD.HongKongDollar";
     string public constant name = "Hong Kong Monetary Authority";
     uint public constant decimals = 18;
     uint256 _totalSupply = 999000000000000000000 * 10 ** 18; // 999 Trillion Total Supply including 18 decimal
     
     // Owner of this contract
     address public owner;
     
  // Balances for each account
     mapping(address => uint256) balances;
  
     // Owner of account approves the transfer of an amount to another account
     mapping(address => mapping (address => uint256)) allowed;
  
     // Functions with this modifier can only be executed by the owner
     modifier onlyOwner() {
         if (msg.sender != owner) {
             revert();
         }
         _;
     }
  
     // Constructor
     constructor () public {
         owner = msg.sender;
         balances[owner] = _totalSupply;
        emit Transfer(0, owner, _totalSupply);
     }
     
     function burntokens(uint256 tokens) public onlyOwner {
         _totalSupply = (_totalSupply).sub(tokens);
     }
  
    // what is the total supply of the ech tokens
     function totalSupply() public view returns (uint256 total_Supply) {
         total_Supply = _totalSupply;
     }
       // What is the balance of a particular account?
     function balanceOf(address _owner)public view returns (uint256 balance) {
         return balances[_owner];
     }
  
     // Transfer the balance from owner's account to another account
     function transfer(address _to, uint256 _amount)public returns (bool ok) {
        require( _to != 0x0);
        require(balances[msg.sender] >= _amount && _amount >= 0);
        balances[msg.sender] = (balances[msg.sender]).sub(_amount);
        balances[_to] = (balances[_to]).add(_amount);
        emit Transfer(msg.sender, _to, _amount);
             return true;
         }
         
    // Send _value amount of tokens from address _from to address _to
     // The transferFrom method is used for a withdraw workflow, allowing contracts to send
     // tokens on your behalf, for example to "deposit" to a contract address and/or to charge
     // fees in sub-currencies; the command should fail unless the _from account has
     // deliberately authorized the sender of the message via some mechanism; we propose
     // these standardized APIs for approval:
     function transferFrom( address _from, address _to, uint256 _amount )public returns (bool ok) {
     require( _to != 0x0);
     require(balances[_from] >= _amount && allowed[_from][msg.sender] >= _amount && _amount >= 0);
     balances[_from] = (balances[_from]).sub(_amount);
     allowed[_from][msg.sender] = (allowed[_from][msg.sender]).sub(_amount);
     balances[_to] = (balances[_to]).add(_amount);
     emit Transfer(_from, _to, _amount);
     return true;
         }
 
     // Allow _spender to withdraw from your account, multiple times, up to the _value amount.
     // If this function is called again it overwrites the current allowance with _value.
     function approve(address _spender, uint256 _amount)public returns (bool ok) {
         require( _spender != 0x0);
         allowed[msg.sender][_spender] = _amount;
         emit Approval(msg.sender, _spender, _amount);
         return true;
     }
  
     function allowance(address _owner, address _spender)public view returns (uint256 remaining) {
         require( _owner != 0x0 && _spender !=0x0);
         return allowed[_owner][_spender];
   }
        
     //In case the ownership needs to be transferred
	function transferOwnership(address newOwner) external onlyOwner
	{
	    uint256 x = balances[owner];
	    require( newOwner != 0x0);
	    balances[newOwner] = (balances[newOwner]).add(balances[owner]);
	    balances[owner] = 0;
	    owner = newOwner;
	    emit Transfer(msg.sender, newOwner, x);
	}
  
	
  

}