import java.util.*;
import java.lang.*;
public class Main{
public static void main(String[] args)
    { 
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        sc.close();
        int[] n = new int[26];
        for(char c:str.toCharArray()){
            n[c-'a']++;
        }
        int min = 21;
        for(int res:n){
            if(res<min&&res>0){
                min = res;
            }
        }
        for(int i=0;i<n.length;i++){
            if(n[i]==min){
                String s1 = ""+(char) ('a'+i);
                str = str.replace(s1,"");
            }
        }
        System.out.println(str);
    }
}