contract Ownable {
  address public owner;

  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

  /**
    * @dev The Ownable constructor sets the original `owner` of the contract to the sender
    * account.
  */
  constructor() public {
    owner = msg.sender;
  }

  /**
    * @dev Throws if called by any account other than the owner.
  */
  modifier onlyOwner() {
    require(msg.sender == owner, "sender is not owner");
    _;
  }

  /**
    * @dev Allows the current owner to transfer control of the contract to a newOwner.
    * @param newOwner The address to transfer ownership to.
  */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0), "newOwner addres is zero");
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}
function transferOwnership(address newOwner) public onlyOwner {
  require(newOwner != address(0), "newOwner addres is zero");
  emit OwnershipTransferred(owner, newOwner);
  owner = newOwner;
}

/**
 * @dev Allows the current owner to transfer control of the contract to a newOwner.
 * @param newOwner The address to transfer ownership to.
 */