import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author cteam024
 */
public class Barrels
{
    static String a = "";
    static List<String> list = new ArrayList<>();
    static int count = 0;
    public static void main(String[] args) throws Exception
    {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String[] input = reader.readLine().split(" ");
        int k = Integer.parseInt(input[2]);
        char[] digits = new char[3];
        digits[0] = input[0].charAt(0);
        digits[1] = input[1].charAt(0);
        digits[2] = input[3].charAt(0);
        combination(0, k, digits);
        System.out.println(count);
        System.exit(0);
    }
    
    static boolean contains(String a)
    {
        for (int i = 0; i < list.size(); i++)
        {
            if (list.get(i).equals(a))
            {
                return true;
            }
        }
        return false;
    }
    
    static int cInString(String a, char c)
    {
        int num = 0;
        for (int i = 0; i < a.length(); i++) {
            if (a.charAt(i) == c)
            {
                num++;
            }
        }
        return num;
    }
    
    static void combination(int index, int k, char[] digits)
    {
        if (index >= k)
        {
            if (!contains(a))
            {
                list.add(a);
                count += cInString(a, digits[2]);
                //System.out.println(a);
            }
            a = a.substring(0, a.length() - 1);
            return;
        }
        for (int i = 0; i < digits.length; i++)
        {
            a += digits[i];
            combination(index + 1, k, digits);
        }
        if (a.length() > 0)
            a = a.substring(0, a.length() - 1);
    }
}