AtCoder Inc. has decided to lock the door of its office with a 3-digit PIN code.

The company has an N-digit lucky number, S. Takahashi, the president, will erase N-3 digits from S and concatenate the remaining 3 digits without changing the order to set the PIN code.

How many different PIN codes can he set this way?

Both the lucky number and the PIN code may begin with a 0.

Constraints

* 4 \leq N \leq 30000
* S is a string of length N consisting of digits.

Input

Input is given from Standard Input in the following format:


N
S


Output

Print the number of different PIN codes Takahashi can set.

Examples

Input

4
0224


Output

3


Input

6
123123


Output

17


Input

19
3141592653589793238


Output

329
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.TreeMap;

public class Main {

    private static PrintWriter out;

    private static void mprintln(Object... ar) {
        for (Object i : ar) {
            out.print(i + " ");
        }
        out.println();
    }

    private static void mprint(Object... ar) {
        for (Object i : ar) {
            out.print(i + " ");
        }
    }

    public static void main(String[] args) throws FileNotFoundException {

        /* Input from file */

        // File inputFile = new File("JavaFile.txt");
        // File outputFile = new File("JavaOutputFile.txt");
        // FileReader fileReader = new FileReader(inputFile);

        /* Here it ends */

        MyScanner sc = new MyScanner(); // Input from console.
        // MyScanner sc = new MyScanner(fileReader); // Input from file.

        out = new PrintWriter(new BufferedOutputStream(System.out)); // Output to console.
        // out = new PrintWriter(new PrintStream(outputFile)); // Output to file.

        int t = 1;
        for (int test = 1; test <= t; ++test)
            getAns(sc);

        out.close();
    }

    /**
     * Don't use built-in function (Math.ceil).
     */
    private static void getAns(MyScanner sc) {
        int n = sc.ni();
        char[] ar = sc.nn().toCharArray();

        HashMap<Character, Integer>[] map = new HashMap[n];
        for (int i = 0; i < n; i++) map[i] = new HashMap<>();

        for (int i = n - 2; i >= 0; i--) {
            map[i] = (HashMap<Character, Integer>) map[i + 1].clone();
            map[i].put(ar[i + 1], i + 1);
        }

//        Arrays.stream(map).forEach(out::println);

        HashSet<Character> done = new HashSet<>();

        long ans = 0;

        for (int i = 0; i < n - 2; i++) {
            if (done.contains(ar[i])) continue;
            done.add(ar[i]);

            for (Map.Entry<Character, Integer> cur: map[i].entrySet()) {
                ans += map[cur.getValue()].size();
            }
        }

        out.println(ans);
    }

    static class MyScanner {

        BufferedReader br;
        StringTokenizer st;

        MyScanner(FileReader fileReader) {
            br = new BufferedReader(fileReader);
        }

        MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String nn() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        String nextLine() {
            String ans = "";
            try {
                ans = br.readLine();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            return ans;
        }

        char nc() {
            return nn().charAt(0);
        }

        int ni() {
            return Integer.parseInt(nn());
        }

        long nl() {
            return Long.parseLong(nn());
        }

        double nd() {
            return Double.parseDouble(nn());
        }

        Integer[] niArr0(int n) {
            Integer[] ar = new Integer[n];
            for (int i = 0; i < n; i++) {
                ar[i] = ni();
            }
            return ar;
        }

        Integer[] niArr1(int n) {
            Integer[] ar = new Integer[n + 1];
            for (int i = 1; i <= n; i++) {
                ar[i] = ni();
            }
            return ar;
        }

        Long[] nlArr0(int n) {
            Long[] ar = new Long[n];
            for (int i = 0; i < n; i++) {
                ar[i] = nl();
            }
            return ar;
        }

        Long[] nlArr1(int n) {
            Long[] ar = new Long[n + 1];
            for (int i = 1; i <= n; i++) {
                ar[i] = nl();
            }
            return ar;
        }
    }
}