pragma solidity 0.4.24;

contract KoET {
  // Highest bidder becomes the Leader.
  // Vulnerable to DoS attack by an attacker contract which reverts all transactions to it.

    address public currentLeader;
    uint public highestBid;

    function () public payable {
        require(msg.value > highestBid && msg.value - highestBid < 1000, "Value have to be within 1000 wei above the highest bit" );
        currentLeader.transfer(highestBid); // Refund the old leader, if it fails then revert
        currentLeader = msg.sender;
        highestBid = msg.value;
    }
}