#include <iostream>
#include <cstring>
using namespace std;


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

    return 0;
}