#include <iostream>
#include <vector>
using namespace std;
int n;


int main()
{
    string s;
    cin >> s;
    int k;
    cin >> k;
    
    int n = s.size();
    string result = "";
    for(int mask = 0; mask < (1 << n); mask++) {
        int broj_na_cifri = 0;
        string tmp = "";
        for(int i = 0; i < n; i++) {
            if(mask & (1 << i)) {
                broj_na_cifri++;
                tmp += s[i];
            }
        }
        if(broj_na_cifri == n - k) {
            result = max(result, tmp);
        }
    }
    cout << result << endl;
    return 0;
}