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.util.*;
import java.io.*;

public class Main {	
	private static void solve(){
		//Implement solution here.
		int n = ni();
		String s = next();
		char[] ca = s.toCharArray();
		int result = 0;
		for(int i = 0; i < 1000; i++) {
			String target = String.format("%03d", i);
			int idx = 0;
			for(int j = 0; j < 3; j++) {
				boolean found = false;
				for(int k = idx; k < n; k++) {
					if(ca[k] == target.charAt(j)) {
						found = true;
						idx = k + 1;
						break;
					}
				}
				if(found) {
					if(j == 2)result++;
					continue;
				} else {
					break;
				}
			}
		}
		System.out.println(result);
	}

	
	//Switch input source (stdin/file)
	private static BufferedReader br;
	public static void main(String[] args){
		br = new BufferedReader(new InputStreamReader(System.in));
		String debugDataPath = System.getenv("DD_PATH");        
		if(debugDataPath != null){
			try{
				br = new BufferedReader(new InputStreamReader(new FileInputStream(new File(debugDataPath))));
			}catch(Exception e){
				throw new RuntimeException(e);
			}
		}
		solve();
	}

	//Input read utility
	private static StringTokenizer tokenizer = null;
	public static String next() {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			try {
				tokenizer = new StringTokenizer(br.readLine());
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
		return tokenizer.nextToken();
	}
	//Get next single int
	private static int ni() {
		return Integer.parseInt(next());
	}
	//Get next single long
	private static long nl() {
		return Long.parseLong(next());
	}
	//Get next single double
	private static double nd() {
		return Double.parseDouble(next());
	}
	//Get next int array from one line
	private static int[] na(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = ni();
		return a;
	}
	//Get next char array from one line
	private static char[] ns() {
		return next().toCharArray();
	}
	//Get next long array from one line
	private static long[] nal(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nl();
		return a;
	}
}