#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <climits>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <regex>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
// #include <atcoder/dsu>

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep1(i, n) for (int i = 1; i <= (int)(n); i++)
#define all(a) a.begin(), a.end()
using namespace std;

template <class T> inline bool chmin(T &a, T b) {
	if (a > b) {
		a = b;
		return true;
	}
	return false;
}
template <class T> inline bool chmax(T &a, T b) {
	if (a < b) {
		a = b;
		return true;
	}
	return false;
}

template <class T1, class T2>
std::ostream &operator<<(std::ostream &out, const pair<T1, T2> &A) {
	cout << "{" << A.first << "," << A.second << "}";
	return out;
}

template <class T1, class T2>
std::ostream &operator<<(std::ostream &out, const map<T1, T2> &M) {
	for (const auto &A : M) {
		cout << "{" << A.first << "," << A.second << "}";
	}
	return out;
}

template <class T1>
std::ostream &operator<<(std::ostream &out, const set<T1> &M) {
	cout << "{";
	for (const auto &A : M) {
		cout << A << ", ";
	}
	cout << "}" << endl;
	return out;
}

template <class T1>
std::ostream &operator<<(std::ostream &out, const multiset<T1> &M) {
	cout << "{";
	for (const auto &A : M) {
		cout << A << ", ";
	}
	cout << "}" << endl;
	return out;
}

template <class T>
std::ostream &operator<<(std::ostream &out, const vector<T> &A) {
	for (const T &a : A) {
		cout << a << " ";
	}
	return out;
}

void print() { cout << endl; }

template <typename Head, typename... Tail> void print(Head H, Tail... T) {
	cout << H << " ";
	print(T...);
}

template <class T> std::istream &operator>>(std::istream &in, vector<T> &A) {
	for (T &a : A) {
		std::cin >> a;
	}
	return in;
}

using ll = long long;
constexpr int INF = numeric_limits<int>::max() / 2;
constexpr ll LINF = numeric_limits<ll>::max() / 2;

vector<vector<int>> com;
int N;
void dfs(vector<int> &A) {
	if (int(A.size()) == 5) {
		com.push_back(A);
		return;
	}
	int f = 0;
	if (not A.empty())
		f = A.back() + 1;
	for (int i = f; i < N; i++) {
		A.push_back(i);
		dfs(A);
		A.pop_back();
	}
}

void solve() {
	// ここからスタート
	cin >> N;
	string S;
	cin >> S;
	vector<int> A(0);
	dfs(A);
	int cnt = 0;
	for (auto &C : com) {
		string T = "";
		for (auto &c : C)
			T.push_back(S[c]);
		bool ok = true;
		if (T[0] != T[2])
			ok = false;
		set<char> st(T.begin(), T.end());
		if (int(st.size()) != 4)
			ok = false;
		if (ok)
			cnt++;
	}
	cout << cnt << endl;
}

int main(void) {
	std::cin.tie(0)->sync_with_stdio(0);
	solve();
	return 0;
}