library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  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;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  /**
  * @dev subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}
/*
 
 
 ███████╗██╗   ██╗██████╗ ███████╗██████╗                                    
 ██╔════╝██║   ██║██╔══██╗██╔════╝██╔══██╗                                   
 ███████╗██║   ██║██████╔╝█████╗  ██████╔╝                                   
 ╚════██║██║   ██║██╔═══╝ ██╔══╝  ██╔══██╗                                   
 ███████║╚██████╔╝██║     ███████╗██║  ██║                                   
 ╚══════╝ ╚═════╝ ╚═╝     ╚══════╝╚═╝  ╚═╝                                   
 
 ██████╗ ██████╗ ██╗   ██╗███╗   ██╗████████╗██████╗ ██╗███████╗███████╗
 ██╔════╝██╔═══██╗██║   ██║████╗  ██║╚══██╔══╝██╔══██╗██║██╔════╝██╔════╝
 ██║     ██║   ██║██║   ██║██╔██╗ ██║   ██║   ██████╔╝██║█████╗  ███████╗
 ██║     ██║   ██║██║   ██║██║╚██╗██║   ██║   ██╔══██╗██║██╔══╝  ╚════██║
 ╚██████╗╚██████╔╝╚██████╔╝██║ ╚████║   ██║   ██║  ██║██║███████╗███████║
 ╚═════╝ ╚═════╝  ╚═════╝ ╚═╝  ╚═══╝   ╚═╝   ╚═╝  ╚═╝╚═╝╚══════╝╚══════╝
 
 
 © 2018 SuperCountries
 
 所有权 - 4CE434B6058EC7C24889EC2512734B5DBA26E39891C09DF50C3CE3191CE9C51E
 
 Xuxuxu - LB - Xufo
 																										   
 */
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;
  }
/**
 * @dev Multiplies two numbers, throws on overflow.
 */