#region memo
/* 
 * 偶奇が大切な問題では、偶数番目と奇数番目を分けて配列に入れる
 * 文字列の処理は遅い。char[]で計算して、最後にstringにする
 * (char)0 は、0'\0'となる
 */
#endregion

using System.Collections;
using System.Text;
using System.Threading.Tasks;
using static System.Math;
using static System.Console;
using System.Collections.Generic;
using System.Linq;
using System;
class Program
{
    static void Main()
    {
        int N =ReadInt();
        string S =ReadStr();
        int count = 0;
        for (int i = 0; i < 10; i++)
        {
            int index1 = -1;
            for (int d = 0; d < N; d++)
            {
                if (S[d]-48 == i)
                {
                    index1 = d;
                    break;
                }
            }
            if (index1 == -1) continue;
            for (int j = 0; j < 10; j++)
            {

                int index2 = -1;
                for (int d = index1+1; d < N; d++)
                {
                    if (S[d] - 48 == j)
                    {
                        index2 = d;
                        break;

                    }
                }
                if (index2 == -1) continue;

                for (int k = 0; k < 10; k++)
                {

                    int index3 = -1;
                    for (int d = index2 + 1; d < N; d++)
                    {
                        if (S[d] - 48 == k)
                        {
                            count++;
                            break; 
                        }
                    }
                    if (index3 == -1) continue;
                }
            }
        }
        WriteLine(count);
        ReadLine();
    }


    static int Divisor(long N)
    {
        int ans = 0;
        int max = (int)Math.Sqrt(N);
        for (int i = 1; i < max; i++)
        {
            if (N % i == 0)
            {
                ans += 2;
            }
        }

        if (N % max == 0)
        {
            if (N / max == max) ans++;
            else
            {
                ans += 2;
            }
        }
        return ans;
    }


    #region Reader
    static string ReadStr()
    {
        return Console.ReadLine();
    }
    static string[] ReadStrN()
    {
        return Console.ReadLine().Split(' ');
    }
    static int ReadInt()
    {
        return Convert.ToInt32(Console.ReadLine());
    }
    static int[] ReadIntN()
    {
        return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray();
    }
    static long ReadLong()
    {
        return Convert.ToInt64(Console.ReadLine());
    }
    static long[] ReadLongN()
    {
        return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray();
    }
    static long[,] ReadLongMatrix(int r, int c)
    {
        var mat = new long[r, c];
        for (int i = 0; i < r; ++i)
        {
            var x = ReadLongN();
            for (int j = 0; j < c; ++j)
            {
                mat[i, j] = x[j];
            }
        }
        return mat;
    }
    static Tuple<string, string>[] ReadTupleStr(int n)
    {
        List<Tuple<string, string>> list = new List<Tuple<string, string>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadStrN();
            list.Add(new Tuple<string, string>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<long, long>[] ReadTupleLong(int n)
    {
        List<Tuple<long, long>> list = new List<Tuple<long, long>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadLongN();
            list.Add(new Tuple<long, long>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<int, int>[] ReadTupleInt(int n)
    {
        List<Tuple<int, int>> list = new List<Tuple<int, int>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadIntN();
            list.Add(new Tuple<int, int>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Tuple<double, double>[] ReadTupleDouble(int n)
    {
        List<Tuple<double, double>> list = new List<Tuple<double, double>>();
        for (int i = 0; i < n; ++i)
        {
            var ab = ReadLongN();
            list.Add(new Tuple<double, double>(ab[0], ab[1]));
        }
        return list.ToArray();
    }
    static Dictionary<int, HashSet<int>> ReadAdjacencyList(int N, int M)
    {
        Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
        for (int i = 0; i <= N; ++i)
        {
            dict.Add(i, new HashSet<int>());
        }
        for (int i = 0; i < M; ++i)
        {
            var ab = ReadIntN();
            dict[ab[0]].Add(ab[1]);
            dict[ab[1]].Add(ab[0]);
        }
        return dict;
    }
    #endregion

}

Measured memory_bytes: 13268