library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint a, uint b) internal pure returns (uint) {
        uint c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }
  function add(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        uint c = a + b;
        require(c >= a, errorMessage);

        return c;
    }

    function sub(uint a, uint b) internal pure returns (uint) {
        return sub(a, b, "LBI::SafeMath: subtraction underflow");
    }
 function sub(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        require(b <= a, errorMessage);
        uint c = a - b;

        return c;
    }
  function mul(uint a, uint b) internal pure returns (uint) {
       if (a == 0) {
            return 0;
        }

        uint c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }
  function mul(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
      if (a == 0) {
            return 0;
        }

        uint c = a * b;
        require(c / a == b, errorMessage);

        return c;
    }
 function div(uint a, uint b) internal pure returns (uint) {
        return div(a, b, "SafeMath: division by zero");
    }
  function div(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }
  function mod(uint a, uint b) internal pure returns (uint) {
        return mod(a, b, "SafeMath: modulo by zero");
    }
  function mod(uint a, uint b, string memory errorMessage) internal pure returns (uint) {
        require(b != 0, errorMessage);
        return a % b;
    }
}
function add(uint a, uint b) internal pure returns (uint) {
        uint c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }
/**
 * @dev Returns the addition of two unsigned integers, reverting on overflow.
 *
 * Counterpart to Solidity's `+` operator.
 *
 * Requirements:
 * - Addition cannot overflow.
 */