import java.util.HashMap;
import java.util.Scanner;
/**
作者:李涵林
/
public class Main26 {public static void main(String[] args) {
Scanner scanner = new Scanner(System.in); outer:while (scanner.hasNext()) { String nextLine = scanner.nextLine(); char[] chars = nextLine.toCharArray(); HashMap<Character, Integer> hashMap = new HashMap(); for (int i = 0; i < chars.length; i++) { char aChar = chars[i]; if (hashMap.containsKey(aChar)) { hashMap.put(aChar, hashMap.get(aChar) + 1); } else { hashMap.put(aChar, 1); } } for (int i = 0; i < chars.length; i++) { char aChar = chars[i]; if (hashMap.get(aChar) == 1) { System.out.println(aChar); continue outer; } } System.out.println(-1); }
}
}