library SafeMath {

    /// @dev Multiplies two numbers, reverts on overflow.
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "MUL_ERROR");

        return c;
    }

    /// @dev Integer division of two numbers truncating the quotient, reverts on division by zero.
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0, "DIVIDING_ERROR");
        uint256 c = a / b;
        return c;
    }

    /// @dev Subtracts two numbers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SUB_ERROR");
        uint256 c = a - b;
        return c;
    }

    /// @dev Adds two numbers, reverts on overflow.
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "ADD_ERROR");
        return c;
    }

    /// @dev Divides two numbers and returns the remainder (unsigned integer modulo), reverts when dividing by zero.
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0, "MOD_ERROR");
        return a % b;
    }
}
/// @dev Math operations with safety checks that revert on error
function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "ADD_ERROR");
        return c;
    }
/// @dev Adds two numbers, reverts on overflow.