#include <bits/stdc++.h>
using namespace std;

int main() {
     string s;
     int k;
     cin >> s >> k;
     int n = s.size();
     int power_of_two = 1;
     for(int i = 0; i < n; i++){
         power_of_two *= 2;
     }
     power_of_two--;
     string answer = "";
     for(int i = 0; i < power_of_two; i++){
         int bin = i;
         int how_many_ones = 0;
         while(bin > 0){
             if(bin % 2 == 1){
                 how_many_ones++;
             }
             bin /= 2;
         }
         if(how_many_ones == n - k){
             bin = i;
             string current_combination = "";
             int j = 0;
             while(bin > 0){
                 if(bin % 2 == 1){
                     current_combination += s[j];
                 }
                 j++;
                 bin /= 2;
             }
             answer = max(answer, current_combination);
         }
     }
     cout << answer << endl;
    return 0;
}