import java.util.Scanner; // 注意类名必须为 Main, 不要有任何 package xxx 信息 public class Main { public static void main(String[] args) { Scanner in = new Scanner(System.in); String s = in.nextLine(); int[] scount = new int[26]; for(int i = 0;i < s.length();i++) { scount[s.charAt(i)-'a'] += 1; } for(int i = 0;i < s.length();i++) { if (scount[s.charAt(i)-'a'] == 1) { System.out.println(s.charAt(i)); return; } } System.out.println(-1); } }