pragma solidity ^0.4.21;

library SafeMath {
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || 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 ERC20Basic {
  uint256 public totalSupply;
  function balanceOf(address who) public constant returns (uint256);
  function transfer(address to, uint256 value) public  returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

contract BasicToken is ERC20Basic {
  using SafeMath for uint256;
  mapping(address => uint256) balances;

  function transfer(address _to, uint256 _value) public returns (bool) {
    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 constant returns (uint256 bal) {
    return balances[_owner];
  }
}

contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender) public constant 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 Token is ERC20, BasicToken {
  mapping (address => mapping (address => uint256)) allowed;
  
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    uint256 _allowance = allowed[_from][msg.sender];
    balances[_to] = balances[_to].add(_value);
    balances[_from] = balances[_from].sub(_value);
    allowed[_from][msg.sender] = _allowance.sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }

  function approve(address _spender, uint256 _value) public returns (bool) {
    assert((_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 remaining) {
    return allowed[_owner][_spender];
  }
}

contract StandardToken is Token {
  string public constant NAME = "Calculator";  
  string public constant SYMBOL = "CL";       
  uint256 public constant DECIMALS = 18;        

  uint256 public constant INITIAL_SUPPLY = 2000000 * 10**18;  

  function StandardToken() public {
    totalSupply = INITIAL_SUPPLY;
    balances[msg.sender] = INITIAL_SUPPLY;
  }
}