#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <limits>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <functional>
#include <iomanip>

using namespace std;

#ifdef LOCAL
#define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
#define eprintf(...) 42
#endif
using ll = long long;
using vll = std::vector<ll>;
using vvll = std::vector<vll>;
using vvvll = std::vector<vvll>;
#define reps(i, S, E) for (ll i = (S); i <= (E); i++)
#define rep(i, N) reps(i, 0, N-1)
#define deps(i, E, S) for (ll i = (E); i >= (S); i--)
#define dep(i, N) deps(i, N-1, 0)
const ll INF = 1LL << 60;
const int INF_INT = 1 << 30;

template<class T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; }return false; }
template<class T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; }return false; }
struct mll {
	static ll MOD;
	ll val;
	mll(ll v = 0) : val(v % MOD) { if (val < 0) val += MOD; }
	mll operator - () const { return -val; }
	mll operator + (const mll &b) const { return val + b.val; }
	mll operator - (const mll &b) const { return val - b.val; }
	mll operator * (const mll &b) const { return val * b.val; }
	mll operator / (const mll &b) const { return mll(*this) /= b; }
	mll operator + (ll b) const { return *this + mll(b); }
	mll operator - (ll b) const { return *this - mll(b); }
	mll operator * (ll b) const { return *this * mll(b); }
	friend mll operator + (ll a, const mll &b) { return b + a; }
	friend mll operator - (ll a, const mll &b) { return -b + a; }
	friend mll operator * (ll a, const mll &b) { return b * a; }
	mll &operator += (const mll &b) { val = (val + b.val) % MOD; return *this; }
	mll &operator -= (const mll &b) { val = (val + MOD - b.val) % MOD; return *this; }
	mll &operator *= (const mll &b) { val = (val*b.val) % MOD; return *this; }
	mll &operator /= (const mll &b) {
		ll c = b.val, d = MOD, u = 1, v = 0;
		while (d) {
			ll t = c / d;
			c -= t * d; swap(c, d);
			u -= t * v; swap(u, v);
		}
		val = val * u % MOD;
		if (val < 0) val += MOD;
		return *this;
	}
	mll &operator += (ll b) { return *this += mll(b); }
	mll &operator -= (ll b) { return *this -= mll(b); }
	mll &operator *= (ll b) { return *this *= mll(b); }
	mll &operator /= (ll b) { return *this /= mll(b); }
	bool operator == (const mll &b) { return val == b.val; }
	bool operator != (const mll &b) { return val != b.val; }
	bool operator == (ll b) { return *this == mll(b); }
	bool operator != (ll b) { return *this != mll(b); }
	friend bool operator == (ll a, const mll &b) { return mll(a) == b.val; }
	friend bool operator != (ll a, const mll &b) { return mll(a) != b.val; }
	friend ostream &operator << (ostream &os, const mll &a) { return os << a.val; }
	friend istream &operator >> (istream &is, mll &a) { return is >> a.val; }
	static mll Combination(ll a, ll b) {
		chmin(b, a - b);
		if (b < 0) return mll(0);
		mll c = 1;
		rep(i, b) c *= a - i;
		rep(i, b) c /= i + 1;
		return c;
	}
};
using vmll = std::vector<mll>;
using vvmll = std::vector<vmll>;
using vvvmll = std::vector<vvmll>;
using vvvvmll = std::vector<vvvmll>;

struct Fast {
	Fast() {
		cin.tie(0);
		ios::sync_with_stdio(false);
		cout << fixed << setprecision(std::numeric_limits<double>::max_digits10);
	}
} fast; //cin,cout高速化のおまじない＋桁数指定

ll mll::MOD = (ll)(1e9 + 7);// 998244353ll;


int main() {
	ll N;
	cin >> N;
	string S;
	cin >> S;
	ll len_S = S.size();
	
	ll result = 0;
	vll keta(3, 0);

	reps(i, 0, 999) {
		keta[0] = i / 100;
		keta[1] = (i % 100) / 10;
		keta[2] = i % 10;

		ll check = 0;
		rep(j, N) {
			if (S[j] - '0' == keta[check]) {
				check++;
				if (check == 3) {
					result++;
					break;
				}
			}
		}
	}

	cout << result << endl;

	return 0;
}

//int main() {
//	ll A;
//	cin >> A;
//	ll B;
//	cin >> B;
//	ll C;
//	cin >> C;
//	ll X;
//	cin >> X;
//	ll Y;
//	cin >> Y;
//
//	ll result = INF;
//	ll stop = max(X, Y);
//
//	reps(i, 0, stop) {
//		ll temp = i * C * 2;
//		temp += max(0ll, X - i) * A;
//		temp += max(0ll, Y - i) * B;
//		chmin(result, temp);
//	}
//
//	cout << result << endl;
//
//	return 0;
//}


////約数の列挙：√N
//vector<ll> Divisor(ll n) {
//	vector<ll> ret;
//	for (ll i = 1; i * i <= n; i++) {
//		if (n % i == 0) {
//			ret.push_back(i);
//			if (i * i != n) {
//				ret.push_back(n / i);
//			}
//		}
//	}
//	std::sort(ret.begin(), ret.end());
//	return (ret);
//}
//
//int main() {
//	ll N;
//	cin >> N;
//
//	ll result = 0;
//
//	reps(i, 1, N) {
//		if (i % 2 == 0) {
//			continue;
//		}
//
//		auto ret = Divisor(i);
//
//		if (ret.size() == 8) {
//			result++;
//		}
//	}
//
//	cout << result << endl;
//
//	return 0;
//}

//int main() {
//	ll N;
//	cin >> N;
//	ll M;
//	cin >> M;
//	vvll A(N, vll(M, 0));
//	rep(i, N) rep(j, M) {
//		cin >> A[i][j];
//	}
//
//	ll result = 0;
//
//	reps(i, 0, M - 2) reps(j, i + 1, M - 1) {
//		ll temp = 0;
//
//		rep(k, N) {
//			temp += max(A[k][i], A[k][j]);
//		}
//
//		chmax(result, temp);
//	}
//
//	cout << result << endl;
//
//	return 0;
//}


Measured memory_bytes: 384