// Vulnerability label: overflow
pragma solidity ^0.4.24;

/**
* @title ERC20 interface
*/
contract ERC20 {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  function approve(address spender, uint256 value) public returns (bool);
  function allowance(address owner, address spender)
    public view returns (uint256);

  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}

/**
 * @title SafeMath
 */
library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
    if (a == 0) {
      return 0;
    }
    c = a * b;
  }

  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    return a / b;
  }

  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 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
} 

/**
 * @title TokenBasic
 */
contract TokenBasic is ERC20 {
    
  using SafeMath for uint256;
  uint256 totalSupply_;

  mapping (address => mapping (address => uint256)) internal allowed;    
  mapping(address => uint256) balances;
  
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  function balanceOf(address _owner) public view returns (uint256) {
    return balances[_owner];
  }         
 
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  function allowance(address _owner, address _spender) public view returns (uint256){
    return allowed[_owner][_spender];
  }

  function increaseApproval(address _spender, uint256 _addedValue) public returns (bool){
    allowed[msg.sender][_spender] = (
      allowed[msg.sender][_spender].add(_addedValue)
    );
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  function decreaseApproval(address _spender, uint256 _subtractedValue) public returns (bool){
    uint256 oldValue = allowed[msg.sender][_spender];
    
    if (_subtractedValue > oldValue) {
      allowed[msg.sender][_spender] = 0;
    } else {
      allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

}

/**
 * @title HBITGOLD COIN
 */
contract HBTG is TokenBasic {
  string public constant name = "HBITGOLD COIN";	
  string public constant symbol = "HBTG";		    
  uint8 public constant decimals = 18;
  uint256 public constant INITIAL_SUPPLY = 3000000000 * (10 ** uint256(decimals));

  constructor() public {
    totalSupply_ = INITIAL_SUPPLY;
    balances[msg.sender] = INITIAL_SUPPLY;
    emit Transfer(address(0), msg.sender, INITIAL_SUPPLY);
  }
}