#include <iostream>
#include <cstring>
#include <cmath>
#include <math.h>
#include <vector>
#include <queue>
using namespace std;

int main()
{
    string s;
    cin >> s;
    int k;
    cin >> k;
    int n = s.size();
    string ans = "";
    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) {
            ans = max(ans, tmp);
        }
    }
    cout << ans << endl;
    return 0;
}