import java.util.*;
import java.io.*;
import java.io.IOException;


public class Question4{


		public static void main (String arg[]){
			    Scanner br= null; 
			    PrintWriter out= null;

				
				
				
				try {

					br = new Scanner(new File("DATA4.txt"));
					out = new PrintWriter(new BufferedWriter(new FileWriter("OUT4.txt")));
					
					  while (br.hasNext() == true) {
						  String line = br.nextLine();
						  for (int i = 0 ; i < line.length(); i ++){
							  if (repeat(line, line.charAt(i), i)){
								  out.write(line.charAt(i) + "\n");
								  break;
							  }
						  }
					  }
						  

				} catch (IOException e) {
					e.printStackTrace();
				}
				
				
				br.close();
				out.close();       

				System.exit(0) ; 
	
		}
		
	public static boolean repeat(String word, char chara, int pos){
		for (int i = 0; i< word.length(); i++){
			if (pos == i)
				continue;
			if (chara == word.charAt(i)){
				return false;
			}
		}
		return true;
	}
}