library SafeMath {
    	/**
    	 * SafeMath mul function
    	 * @dev function for safe multiply, throws on overflow.
    	 **/
    	function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    		uint256 c = a * b;
    		assert(a == 0 || c / a == b);
    		return c;
    	}
    
    	/**
    	 * SafeMath div funciotn
    	 * @dev function for safe devide, throws on overflow.
    	 **/
    	function div(uint256 a, uint256 b) internal pure returns (uint256) {
    		uint256 c = a / b;
    		return c;
    	}
    
    	/**
    	 * SafeMath sub function
    	 * @dev function for safe subtraction, throws on overflow.
    	 **/
    	function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    		assert(b <= a);
    		return a - b;
    	}
    	
    	/**
    	 * SafeMath add function
    	 * @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
 * @notice https://github.com/OpenZeppelin/zeppelin-solidity/blob/master/contracts/math/SafeMath.sol
 */
function sub(uint256 a, uint256 b) internal pure returns (uint256) {
	assert(b <= a);
	return a - b;
}

/**
 	 * SafeMath sub function
 	 * @dev function for safe subtraction, throws on overflow.
 	 **/