pragma solidity ^0.4.24;

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) {
      require(_b > 0);
      uint256 c = _a / _b;
      return c;
  }

  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
      assert(_b <= _a);
      uint256 c = _a - _b;
      return c;
  }

  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 (uint256);
  function balanceOf(address _who) public view returns (uint256);
  function allowance(address _owner, address _spender) public view returns (uint256);
  function transfer(address _to, uint256 _value) public returns (bool);
  function approve(address _spender, uint256 _value) public returns (bool);
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
  event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract StandardToken is ERC20 {
  using SafeMath for uint256;

  mapping(address => uint256) balances;
  mapping (address => mapping (address => uint256)) internal allowed;
  uint256 totalSupply_;

  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  function balanceOf(address _owner) public view returns (uint256) {
    return balances[_owner];
  }

  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }

  function transfer(address _to, uint256 _value) public returns (bool) {
    require(_value <= balances[msg.sender]);
    require(_to != address(0));

    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _to, _value);
    return true;
  }

  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }
}

contract USHCToken is StandardToken{
    using SafeMath for uint256;
    
    string public name="USHCToken";
    string public symbol="USHC";
    uint256 public decimals=18;
    address owner;
    
    event Burn(uint256 amount);

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    constructor(uint256 initialSupply) public {
        totalSupply_ = initialSupply * (10 ** decimals);
        balances[msg.sender]=totalSupply_;
        owner=msg.sender;
    }
    
    function burn(uint256 _amount) onlyOwner public returns (bool) {
        require(0 < _amount && _amount <= balances[msg.sender]);
        balances[msg.sender] = balances[msg.sender].sub(_amount);
        totalSupply_ = totalSupply_.sub(_amount);
        emit Burn(_amount);
        return true;
    }
    
    function transferOwnership(address newOwner) onlyOwner public {
        _transferOwnership(newOwner);
    }
    
    function _transferOwnership(address newOwner) internal {
        owner = newOwner;
    }
}