/******************************************************************************
 * Program computes a simple checksum of STDIN
 * 
 * Copyright © 2017 Richard Lesh.  All rights reserved.
 *****************************************************************************/

import org.pureprogrammer.Utils;

public class SimpleChecksum1 {

    public static void main(String[] args) {
        int c;
        int checksum = 0;
        while ((c = Utils.getbyte(System.in)) != -1) {
            checksum ^= c;
        }
        System.out.println(Utils.format("{0:02X}", checksum));
    }
}