#if 1
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <queue>
#include <stack>
#include <array>
#include <deque>
#include <algorithm>
#include <utility>
#include <cstdint>
#include <functional>
#include <iomanip>
#include <numeric>
#include <assert.h>
#include <bitset>
#include <list>
#include <cmath>
#ifdef _MSC_VER
#pragma warning( push )
#pragma warning( disable : 26450 )
#pragma warning( disable : 26451 )
#pragma warning( disable : 26498 )
#pragma warning( disable : 4459 )
#endif
#include <atcoder/all>
#ifdef _MSC_VER
#pragma warning( pop )
#endif

auto& in = std::cin;
auto& out = std::cout;
#define all_range(C) std::begin(C), std::end(C)
const double PI = 3.141592653589793238462643383279502884197169399375105820974944;

int countr[40][40] = {};

int main()
{
	using std::endl;
	in.sync_with_stdio(false);
	out.sync_with_stdio(false);
	in.tie(nullptr);
	out.tie(nullptr);

	int n;
	in >> n;
	std::string S;
	in >> S;
	std::reverse(S.begin(), S.end());
	for (int i = S.size() - 1; i >= 0; --i) {
		if (i >= 40) { throw 0; }
		for (int j = 0; j < 40; j++) {
			countr[i][j] = countr[i+1][j];
		}
		countr[i][S[i] - 'A'] += 1;
	}

	int64_t count_sum = 0;
	for (size_t i = 0; i < S.size(); i++)
		for (size_t j = i + 1; j < S.size(); j++) if (S[i] != S[j])
			for (size_t k = j + 1; k < S.size(); k++) if (S[i] != S[k] && S[j] != S[k])
				for (size_t l = k + 1; l < S.size(); l++) if (S[i] != S[l] && S[j] != S[l] && S[k] != S[l])
	{
		count_sum += countr[l + 1][S[k] - 'A'];
	}

	out << count_sum << endl;
}
#endif