contract Lock {
  address owner;
  uint unlockTime;

  constructor(uint _t) payable {
    owner = msg.sender;
    unlockTime = _t;
  }

  function withdraw() public {
    require(block.timestamp >= unlockTime,
            "too early");
    require(msg.sender == owner,
            "not owner");
    payable(owner).transfer(address(this).balance);
  }
}