#include<fstream>
#include<string.h>
using namespace std;
string resWord, curWord, alphabet;
int counter=0, k, n, len;
bool isReady=0;
bool isInterest(string s)
{
    bool interest=1;
    int l=s.length();
    string clone(s);
    //cout<<clone<<endl;
    char help;
    for(int i=0; i<l-1; ++i)
    {
        help=s[0];
        for(int j=0; j<l-1; ++j)s[j]=s[j+1];
        s[l-1]=help;
        //cout<<"    "<<s<<endl;
        if(clone>=s){ interest=0; break; }
    }
    return interest;
}
void generateWords(int ind, int let)
{
    //cout<<ind<<" "<<let<<endl;
    if(isReady)return;
    if(let==k)
    {
        if(isInterest(curWord))
        {
            counter++;
            if(counter==n)
            {
                resWord=curWord;
                isReady=1;
            }
        }
        return;
    }
    curWord[let]=alphabet[ind];
    for(int i=ind; i<len; i++)
    {
        generateWords(i, let+1);
    }
    //return;
}
int main()
{
    //stirng alphabet;
    ifstream inpf("nthword.in", ios::in);
    inpf>>alphabet;
    len=alphabet.length();
    //int k, n;
    inpf>>k>>n;
    inpf.close();
    curWord=string(k, '\0');
    generateWords(0, 0);
    ofstream outf("nthword.out", ios::out);
    outf<<resWord<<endl;
    outf.close();
    return 0;
}