/*
ID:   cs_diab1
TASK: 
LANG: C++
*/

#include <map>
#include <set>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cctype>
#include <cstdio>
#include <limits>
#include <string>
#include <vector>
#include <cassert>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <numeric>
#include <sstream>
#include <utility>
#include <iostream>
#include <algorithm>
#include <functional>
#include <conio.h>

#define stop exit(0)
#define nc -1
#define eps 1e-10
#define inf 1000000000
#define mod 1000000007
#define mp make_pair

#define fill(array,value) memset(array,value,sizeof(array))
#define f(i,beg,end) for(int i=beg; i<=end; i++)
#define F(i,beg,end) for(int i=beg; i>=end; i--)
#define Max(a,b) ( (a>b)?a:b )
#define Min(a,b) ( (a<b)?a:b )
#define pi 3.1415926535897932384626433832
#define iread(var) scanf("%d",&var)
#define dread(var) scanf("%f",&var)
#define lread(var) scanf("%lld",&var)
#define input(name) freopen(name,"r",stdin)
#define output(name) freopen(name,"w",stdout)
typedef unsigned long long ull;
typedef unsigned int ui;
typedef long double ld;
typedef long long ll;

using namespace std;

string azbuka, sol, curr;
int m, n, k, cnt=0;

void redirect()
{
    input("nthword.in");
    output("nthword.out");
}

void generate(int pos, int strictlyMonotonous)
{
    //cout<<cnt<<" "<<curr<<" "<<pos<<endl; getch();
    //cout<<pos<<endl;
    if (pos==k)
    {
        if (!strictlyMonotonous) return;
        
        cnt++;
        //cout<<cnt<<" : "<<curr<<endl;
        if (cnt==n)
        {
            cout<<curr<<endl;
            stop;
        }
        return;
    }
    
    if (pos==0)
    {
        f(i,0,m-1)
        {
            curr[pos]=azbuka[i];
            generate(pos+1,0);
        }
    }
    else 
    {
        f(i,0,m-1)
            if (azbuka[i]==curr[pos-1])
            {
                curr[pos]=azbuka[i];
                generate(pos+1,strictlyMonotonous);
            }
            else 
                if (azbuka[i]>curr[pos-1])
                {
                    curr[pos]=azbuka[i];
                    generate(pos+1,1);
                }
    }
}

void init()
{
    cin>>azbuka; m=azbuka.size();
    //cin>>n>>k;
    cin>>k>>n;
    
    //cout<<azbuka<<" "<<n<<" "<<k<<endl;
    
    curr.resize(k); sol.resize(k);
    generate(0,0);     // curr_str curr_pos bit
}

int main()
{
    redirect();
    //input("test.txt");
    init();

    return 0;
}<!-- 0.0412s -->