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.BufferedWriter;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.PrintWriter;
import java.lang.reflect.Array;
import java.math.BigDecimal;
import java.math.MathContext;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
import java.util.Scanner;
import java.util.Set;
import java.util.Stack;
import java.util.TreeMap;
import java.util.TreeSet;

import static java.util.Comparator.*;

public class Main {
    public static void main(String[] args) {
        PrintWriter out = new PrintWriter(System.out);
        Solver solver = new Solver(System.in, out);
        solver.solve();
        out.close();
    }
}
class Solver {
	Scanner sc;
	PrintWriter out;
    public Solver(InputStream in, PrintWriter out) {
    	sc = new Scanner(in);
    	this.out = out;
    }
    // ======================================================================
    int[][] P = new int[30010][10];
    public void solve() {
    	int N = ni();
    	char[] C = ns().toCharArray();
    	int[] m = new int[10];
    	Arrays.fill(m, -1);
    	Arrays.fill(P[N], -1);
    	int wk;
    	for (int i = N-1; i >= 0; i--) {
    		wk = (int)(C[i]-'0');
//    		out.println("wk = " + wk + "  i = " + i);
    		m[wk] = i+1;
    		for (int j = 0; j < 10; j++) {
    			P[i][j] = m[j];
			}
		}
//    	for (int i = 0; i <= N; i++) {
//    		for (int j = 0; j < 10; j++) {
//				out.print((P[i][j] == -1 ? "* " : P[i][j] + " "));
//			}
//    		out.println("");
//		}
    	Set<Integer> set = new HashSet<>();
    	int next_1, next_2;
    	for (int n = 0; n < N-2; n++) {
	    	for (int i = 0; i < 10; i++) {
//				out.println("　１　数字[" + i + "]  P[" + n + "][" + i + "] = " + P[n][i]);
				if(P[n][i] == -1)		continue;
				next_1 = P[n][i];
				for (int j = 0; j < 10; j++) {
//					out.println("　２　数字[" + j + "]  P[" + next_1 + "][" + j + "] = " + P[next_1][j]);
					if(P[next_1][j] == -1)	continue;
					next_2 = P[next_1][j];
					for (int j2 = 0; j2 < 10; j2++) {
//						out.println("　３　数字[" + j2 + "]  P[" + next_2 + "][" + j2 + "] = " + P[next_2][j2]);
						if(P[next_2][j2] == -1)	continue;
						set.add(i*100 + j * 10 + j2);
//						out.println("  見つかった  [" + i + " " + j + " " + j2 + " ]");
					}
				}
			}
    	}
    	out.println(set.size());
    }
    // ------------------------------------------
    // 入力
    // ------------------------------------------
    public int ni() {
    	return sc.nextInt();
    }
    public long nl() {
    	return sc.nextLong();
    }
    public String ns() {
    	return sc.next();
    }
    public char[] nc() {
    	return sc.next().toCharArray();
    }
    public int[] ndi(int N) {
    	int[] ans = new int[N];
    	for (int i = 0; i < N; i++) {
			ans[i] = ni();
		}
    	return ans;
    }
    public long[] ndl(int N) {
    	long[] ans = new long[N];
    	for (int i = 0; i < N; i++) {
			ans[i] = nl();
		}
    	return ans;
    }
    public String[] nds(int N) {
    	String[] ans = new String[N];
    	for (int i = 0; i < N; i++) {
			ans[i] = ns();
		}
    	return ans;
    }
    public char[][] ndc(int N) {
    	char[][] ans = new char[N][];
    	for (int i = 0; i < N; i++) {
			ans[i] = nc();
		}
    	return ans;
    }
    public int[][] nddi(int N, int S) {
    	int[][] ans = new int[N][S];
    	for (int i = 0; i < N; i++) {
			for (int j = 0; j < S; j++) {
				ans[i][j] = ni();
			}
		}
    	return ans;
    }
}
