library SafeMath {
	/**
	* @dev Multiplies two unsigned integers, reverts on overflow.
	*/
	function mul(uint256 a, uint256 b) internal pure returns (uint256) {
		// Gas optimization: this is cheaper than requiring 'a' not being zero, but the
		// benefit is lost if 'b' is also tested.
		// See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
		if (a == 0) {
			return 0;
		}

		uint256 c = a * b;
		require(c / a == b, "SafeMath: multiplication overflow");

		return c;
	}

	/**
	* @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
	*/
	function div(uint256 a, uint256 b) internal pure returns (uint256) {
		// Solidity only automatically asserts when dividing by 0
		require(b > 0, "SafeMath: division by zero");
		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 unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
	*/
	function sub(uint256 a, uint256 b) internal pure returns (uint256) {
		require(b <= a, "SafeMath: subtraction overflow");
		uint256 c = a - b;

		return c;
	}

	/**
	* @dev Adds two unsigned integers, reverts on overflow.
	*/
	function add(uint256 a, uint256 b) internal pure returns (uint256) {
		uint256 c = a + b;
		require(c >= a, "SafeMath: addition overflow");

		return c;
	}

	/**
	* @dev Divides two unsigned integers 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, "SafeMath: modulo by zero");
		return a % b;
	}
}
/**
 * @title SafeMath
 * @dev Unsigned 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, "SafeMath: addition overflow");

		return c;
	}
/**
 	* @dev Adds two unsigned integers, reverts on overflow.
 	*/