library SafeMath {
    /**
     * mul
     * @dev Safe math multiply function
     */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }
  /**
   * add
   * @dev Safe math addition function
   */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}
/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
/**
 * add
 * @dev Safe math addition function
 */