import java.util.*;
import java.lang.*;
import java.io.*;
class Main{
    static class Pair{
        char first;
        int second;
        Pair(char first,int second){
            this.first=first;
            this.second=second;
        }
    }
    public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
        TreeMap<Character,Integer> m = new TreeMap<>();    
        String s=sc.next();
        int k=sc.nextInt();
        for(int i=0;i<s.length();i++){
            char ch = s.charAt(i);
            int x=0;
            if(m.containsKey(ch))
                x=m.get(ch);
            m.put(ch,x+1);
        }
        ArrayList<Pair> list = new ArrayList<Pair>();
        for(Map.Entry<Character,Integer> i : m.entrySet()){
            list.add(new Pair(i.getKey(),i.getValue()));
        }
        Collections.sort(list, (a,b)->{if(a.second>=b.second) return -1; else return 1;});
        System.out.println(list.get(k-1).first);
        
    }

}