// Vulnerability label: locked
pragma solidity ^0.4.18;

contract Ownable {
    address public owner;
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    function Ownable() public {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0));
        OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

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) {
        uint256 c = a / b;
        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 ERC20Token {
    using SafeMath for uint256;

    string public name;
    string public symbol;
    uint256 public decimals;
    uint256 public totalSupply;

    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

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

    function ERC20Token (
        string _name, 
        string _symbol, 
        uint256 _decimals, 
        uint256 _totalSupply) public 
    {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        totalSupply = _totalSupply * 10 ** decimals;
        balanceOf[msg.sender] = totalSupply;
    }

    function _transfer(address _from, address _to, uint256 _value) internal {
        require(_to != 0x0);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to].add(_value) > balanceOf[_to]);
        uint256 previousBalances = balanceOf[_from].add(balanceOf[_to]);
        balanceOf[_from] = balanceOf[_from].sub(_value);
        balanceOf[_to] = balanceOf[_to].add(_value);

        Transfer(_from, _to, _value);
        assert(balanceOf[_from].add(balanceOf[_to]) == previousBalances);
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);
        allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }
}

contract JumboToken is Ownable, ERC20Token {
    event Burn(address indexed from, uint256 value);

    function JumboToken (
        string name, 
        string symbol, 
        uint256 decimals, 
        uint256 totalSupply
    ) ERC20Token (name, symbol, decimals, totalSupply) public {}

    function() payable public {
        revert();
    }

    function burn(uint256 _value) onlyOwner public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] = balanceOf[msg.sender].sub(_value);
        totalSupply = totalSupply.sub(_value);
        Burn(msg.sender, _value);
        return true;
    }
}