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.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Main {
	public static void main(String args[]) throws IOException {
		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
		Solver solver = new Solver();
		solver.init();
		solver.readHead(in.readLine());
		solver.readS(in.readLine());
		// for (; solver.hasNext();) {
		// solver.readBody(in.readLine());
		// }
		// solver.solve();
	}
}

class Solver {
	int N;
	int cnt;

	public void init() {
		N = 0;
		cnt = 0;
	}

	public void readHead(String str) {
		String[] strArr = str.split("\\s+");
		N = Integer.parseInt(strArr[0]);
		// System.out.println(N);
	}

	public void readS(String str) {
		S = str;
		System.out.println(check(3, 0));
	}

	String S;

	private int check(int digi, int left) {
		if (digi < 1)
			return 0;
		if (left >= N)
			return 0;
		int ans = 0;
		for (char c = '0'; c <= '9'; c++) {
			for (int pos = left; pos < N; pos++) {
				if (S.charAt(pos) != c)
					continue;
				// System.out.println(digi + " " + c + " " + pos);
				if (digi == 1)
					ans += 1;
				else
					ans += check(digi - 1, pos + 1);
				break;
			}
		}
		return ans;
	}

	public boolean hasNext() {
		return cnt < N;
	}

	public void readBody(String str) {
		// System.out.println(str);
		cnt++;
	}

	public void solve() {

	}
}
