### BUGGY CODE ###

# /usr/bin/python3
# -*- coding: utf-8 -*-
from queue import Queue
from queue import LifoQueue as Stack
from math import sqrt, floor, ceil, log2, log10, pi
from fractions import gcd
from itertools import permutations, combinations
from operator import itemgetter
from functools import cmp_to_key


INF=1001001001
__MOD__=(10**9)+7
yn = 'YNeos'
judge = False
cnt = 0
ans = None


def lcm(a, b):
    return (a*b) // gcd(a,b)

def intinput():
    return int(input())

def mulinputs():
    return map(int,input().split())

def lineinputs(func=intinput):
    datas = []
    while True:
        try:
            datas.append(func())
        except EOFError:
            break
    return datas

class ModInt():
    def __init__(self, x):
        self.__x = (x % __MOD__)
    def __add__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((self.__x + other.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((self.__x + other.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")
    def __radd__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((other.__x + self.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((other.__x + self.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")

    def __sub__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((self.__x - other.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((self.__x - other.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")
    def __rsub__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((other.__x - self.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((other.__x - self.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")

    def __mul__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((self.__x * other.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((self.__x * other.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")
    def __rmul__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((other.__x * self.__x)%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((other.__x * self.__x)%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")

    def __truediv__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((self.__x * other.__modinv())%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((self.__x * other.__modinv())%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")
    def __rtruediv__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__((other.__x * self.__modinv())%__MOD__))
        elif type(other) == ModInt:
            return self.__class__((other.__x * self.__modinv())%__MOD__)
        else:
            raise Exception("Not Int or Not ModInt")

    def __pow__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__(pow(self.__x, other.__x, __MOD__)))
        elif type(other) == ModInt:
            return self.__class__(pow(self.__x, other.__x, __MOD__))
        else:
            raise Exception("Not Int or Not ModInt")
    def __rpow__(self, other):
        if type(other) == int:
            other = self.__class__(other)
            return int(self.__class__(pow(other.__x, self.__x, __MOD__)))
        elif type(other) == ModInt:
            return self.__class__(pow(other.__x, self.__x, __MOD__))
        else:
            raise Exception("Not Int or Not ModInt")

    def __modinv(self, m=__MOD__):
        a = self.__x
        if a == 0:
            raise ZeroDivisionError()
        if gcd(a, m) != 1:
            raise Exception("%sの逆数は求まりません。" % a)
        b, u, v = m, 1, 0
        while b != 0:
            t = a//b;
            a -= t*b
            a, b = b, a
            u -= t * v
            u, v = v, u
        u %= m
        if u < 0:
            u += m
        return u
    def __int__(self):
        return self.__x
    def __str__(self):
        return str(self.__x)



if __name__ == '__main__':
    N = intinput()
    S = input()
    # org = [i for i in set(S)]
    # ans_set = []
    # org.sort()
    # for c in org:
    #     for cc in org:
    #         for ccc in org:
    #             ans_set.append(c+cc+ccc)
    # b = [None] * len(S)
    # b[0] = set()
    # for i in range(1, len(S)):
    #     b[i] = set(S[i:])
    ans_set = []
    pset = [i for i in set(S)]
    # pset = [str(i) for i in range(10)]
    for p1 in pset:
        for p2 in pset:
            for p3 in pset:
                ans_set.append(p1+p2+p3)
    # ans_set.sort()
    cnt = 0
    last = len(S)
    for ans in ans_set:
        idx = 0
        fidx, sidx, tidx = -1, -1, -1
        is_hit = False
        for i in range(last):
            # print(i, S[i], ans[idx])
            # if idx < 3:
            #     if S[i] == ans[idx]:
            #         idx += 1
            #     continue
            # else:
            #     print(ans)
            #     is_hit = True
            #     break
            if fidx < 0:
                if S[i] == ans[0]:
                    fidx = i
                continue
            if sidx < 0:
                if S[i] == ans[1]:
                    sidx = i
                if i == last-1:
                    break
                continue
            if tidx < 0:
                if S[i] == ans[2]:
                    is_hit = True
                    break
        if is_hit:
            cnt += 1
    # 出力
    print(cnt)


### FIXED CODE ###

import copy
import math
import time
 
# a = get_int()
def get_int():
    return int(input())
# a = get_string()
def get_string():
    return input()
# a_list = get_int_list()
def get_int_list():
    return [int(x) for x in input().split()]
# a_list = get_string_list():
def get_string_list():
    return input().split()
# a, b = get_int_multi()
def get_int_multi():
    return map(int, input().split())
# a_list = get_string_char_list()
def get_string_char_list():
    return list(str(input()))
# print("{} {}".format(a, b))
# for num in range(0, a):
# a_list[idx]
# a_list = [0] * a
'''
while (idx < n) and ():
 
    idx += 1
'''
 
def main():
    start = time.time()
 
    n = get_int()
    s_list = get_string_char_list()
    s_list = [int(x) for x in s_list]
 
    #n = 30000
    #s_list = [1] * 30000
 
    #ans_set = set([])
 
    #for i in range(0,n):
    #    for ii in range(i+1, n):
    #        for iii in range(ii+1, n):
    #            ans_set.add(int(s_list[i]) * 100 + int(s_list[ii]) * 10 + int(s_list[iii]) * 1)
 
    #print(len(ans_set))
 
    ans = 0
 
    for i in range(0, 1000):
        a = i // 100
        b = (i % 100) // 10
        c = i % 10
 
        find_a = False
        find_b = False
        for ii in s_list:
 
            if (find_a == False) and (ii == a):
                find_a = True
            elif (find_a == True) and (find_b == False) and (ii == b):
                find_b = True
            elif (find_b == True) and (ii == c):
 
                ans += 1
                break
    print(ans)
 
    #print(time.time() - start)
 
if __name__ == '__main__':
    main()