library SafeMath {
        /**
        * @dev Multiplies two numbers, throws on overflow.
        */
        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;
        }
    
        /**
        * @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 a / b;
        }
    
        /**
        * @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 c) {
            c = a + b;
            assert(c >= a);
            return c;
        }
    }
/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
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 a / b;
        }
/**
 * @dev Integer division of two numbers, truncating the quotient.
 */