pragma solidity ^0.4.24;


library SafeMath 
{

 
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256 c) {
    
    if (_a == 0) {
      return 0;
    }

    c = _a * _b;
    assert(c / _a == _b);
    return c;
  }

  
  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;
  }
  
}


contract Ownable 
{
  address public owner;

  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );

  
  constructor() public {
    owner = msg.sender;
  }

 
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  
  function transferOwnership(address _newOwner) public onlyOwner {
    _transferOwnership(_newOwner);
  }

  
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
  
}



contract Pausable is Ownable 
{
  event Pause();
  event Unpause();

  bool public paused = false;

  
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

 
  modifier whenPaused() {
    require(paused);
    _;
  }

  
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    emit Pause();
  }

  
  function unpause() onlyOwner whenPaused public {
    paused = false;
    emit Unpause();
  }

}


contract ERC20Basic 
{
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}


contract ERC20 is ERC20Basic 
{
  function allowance(address owner, address spender) public view returns (uint256);

  function transferFrom(address from, address to, uint256 value) public returns (bool);

  function approve(address spender, uint256 value) public returns (bool);
  
  event Approval(
    address indexed owner,
    address indexed spender,
    uint256 value
  );

}


contract BasicToken is ERC20Basic 
{
  using SafeMath for uint256;

  mapping(address => uint256) balances;

  uint256 totalSupply_;

 
  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];
  }

}



contract StandardToken is ERC20, BasicToken 
{

  mapping (address => mapping (address => uint256)) internal allowed;

 
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    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;
  }

 
  function approve(address _spender, uint256 _value) public returns (bool) {
    require((_value == 0) || (allowed[msg.sender][_spender] == 0));
    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;
  }

}



contract PausableToken is StandardToken, Pausable 
{

  function transfer(address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transfer(_to, _value);
  }

  function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transferFrom(_from, _to, _value);
  }

  function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {
    return super.approve(_spender, _value);
  }

  function increaseApproval(address _spender, uint256 _addedValue) public whenNotPaused returns (bool success) {
    return super.increaseApproval(_spender, _addedValue);
  }

  function decreaseApproval(address _spender, uint256 _subtractedValue) public whenNotPaused returns (bool success) {
    return super.decreaseApproval(_spender, _subtractedValue);
  }

}



contract FrozenableToken is Ownable 
{
    
    mapping (address => bool) public frozenAccount;

    event FrozenFunds(address indexed to, bool frozen);

    modifier whenNotFrozen(address _who) {
      require(!frozenAccount[msg.sender] && !frozenAccount[_who]);
      _;
    }

    function freezeAccount(address _to, bool _freeze) public onlyOwner {
        require(_to != address(0));
        frozenAccount[_to] = _freeze;
        emit FrozenFunds(_to, _freeze);
    }

}


contract shells is PausableToken, FrozenableToken 
{

    string public name = "shells.exchange";
    string public symbol = "SHL";
    uint256 public decimals = 18;
    uint256 INITIAL_SUPPLY = 13860116124560492194807950;

  
    constructor() public {
        totalSupply_ = INITIAL_SUPPLY;
        balances[msg.sender] = totalSupply_;
        emit Transfer(address(0), msg.sender, totalSupply_);
    }

   
    function() public payable {
        revert();
    }

  
    function transfer(address _to, uint256 _value) public whenNotFrozen(_to) returns (bool) {
        return super.transfer(_to, _value);
    }

 
    function transferFrom(address _from, address _to, uint256 _value) public whenNotFrozen(_from) returns (bool) {
        return super.transferFrom(_from, _to, _value);
    }        
    
}