Problem:
Score: 400 points

Problem Statement

AtCoder Inc. has decided to lock the door of its office with a 3-digit PIN code.

The company has an N-digit lucky number, S. Takahashi, the president, will erase N-3 digits from S and concatenate the remaining 3 digits without changing the order to set the PIN code.

How many different PIN codes can he set this way?

Both the lucky number and the PIN code may begin with a 0.

Constraints

4 \leq N \leq 30000

S is a string of length N consisting of digits.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the number of different PIN codes Takahashi can set.

Sample Input 1

4
0224

Sample Output 1

3

Takahashi has the following options:

Erase the first digit of S and set 224.

Erase the second digit of S and set 024.

Erase the third digit of S and set 024.

Erase the fourth digit of S and set 022.

Thus, he can set three different PIN codes: 022, 024, and 224.

Sample Input 2

6
123123

Sample Output 2

17

Sample Input 3

19
3141592653589793238

Sample Output 3

329

Solution in C++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <vector>
#include <deque>
#include <algorithm>
#include <numeric>
#include <string>
#include <cstring>
#include <list>
#include <unordered_set>
#include <tuple>
#include <cmath>
#include <limits>
#include <type_traits>
#include <iomanip>
#include <unordered_map>
#include <queue>
#include <stack>
#include <set>
#include <bitset>
#include <regex>
using namespace std;

#define rep(i,n)	for(lint i = 0; i < n; i++)
#define repr(i,n)	for(lint i = n - 1; i >= 0; i--)
#define repi(i,ini,n)	for(lint i = ini; i < n; i++)
#define repir(i,ini,n)	for(lint i = n-1; i >= ini; i--)
#define repb(i,start,end)	for(lint i = start; i <= end; i++)
#define repbr(i,start,end)	for(lint i = end; i >= start; i--)

#define bit(n)				(1LL << n)
#define brep(i, n)			rep(i, bit(n))
#define brepi(i, ini, n)	repi(i, ini, bit(n))

#define len(a)	(static_cast<lint>(a.size()))

#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define rg(v, n) v.begin(), v.begin()+n
#define rrg(v, n) v.rbegin(), v.rbegin()+n

#define ret return 0;

namespace {

	using lint = long long;
	using ulint = unsigned long long;
	using ld = long double;
	struct xy
	{
		lint x, y;
		xy() :x(0), y(0) {}
		xy(lint _x, lint _y) : x(_x), y(_y) {}
		xy operator+(const xy& p) const
		{
			return xy(x + p.x, y + p.y);
		}
		bool operator<(xy p) const
		{
			if (y == p.y)
				return x < p.x;
			return y < p.y;
		}
	};
	struct xyd
	{
		ld x, y;
		xyd() :x(0), y(0) {}
		xyd(long double _x, long double _y) : x(_x), y(_y) {}
	};
	using vec = vector<lint>;
	using vecd = vector<ld>;
	using vecs = vector<string>;
	using vecp = vector<xy>;
	template<class T> using vect = vector<T>;
	class vec2 : public vector<vector<lint>>
	{
	public:
		vec2() {}
		vec2(lint n) : vector(n) {}
		vec2(lint h, lint w) : vector(h, vector<lint>(w)) {}
		vec2(lint h, lint w, lint v) : vector(h, vector<lint>(w, v)) {}
	};

	template<class T> using priq = priority_queue<T>;
	template<class T> using rpriq = priority_queue<T, vector<T>, greater<T>>;

	//const ulint mod = 1000000007;
	const ulint mod = 998244353;
	const double pi = 3.141592653589793238462;
	const lint intmax = 9223372036854775807;
	const lint inf = 1100100100100100100LL;
	const ld eps = 0.0000001;
	const lint alpn = 'z' - 'a' + 1;

	template<class T>
	constexpr auto msum(T arg0)
	{
		return arg0;
	}

	template<class T, class ...Types>
	constexpr auto msum(T arg0, Types ...args)
	{
		static_assert(sizeof...(args) > 0, "arg err");

		return arg0 + msum(args...);
	}

	template<class It>
	constexpr typename It::value_type mmax(It begin, It end)
	{
		return *max_element(begin, end);
	}

	template<class It>
	constexpr typename It::value_type mmin(It begin, It end)
	{
		return *min_element(begin, end);
	}

	template<class T>
	constexpr auto mmax(T arg)
	{
		return arg;
	}

	template<class T, class ...Types>
	constexpr auto mmax(T arg0, Types ...args)
	{
		using promote_t = decltype(msum(arg0, args...));

		return max(static_cast<promote_t>(arg0), static_cast<promote_t>(mmax(args...)));
	}

	template<class T>
	constexpr auto mmin(T arg)
	{
		return arg;
	}

	template<class T, class ...Types>
	constexpr auto mmin(T arg0, Types ...args)
	{
		using promote_t = decltype(msum(arg0, args...));

		return min(static_cast<promote_t>(arg0), static_cast<promote_t>(mmin(args...)));
	}

	template<class T>
	struct Mplus
	{
		T operator()(const T& a, const T& b)
		{
			return a + b;
		}

		const static T id = T(0);
	};

	template<
		class It,
		class T = typename It::value_type,
		class Monoid = Mplus<T>>
		T acc(It begin, It end, Monoid f = Mplus<T>())
	{
		return accumulate(begin, end, Monoid::id, f);
	}

	constexpr auto clamp(lint val, lint left, lint right)
	{
		return mmax(mmin(val, right), left);
	}

	constexpr lint div2(lint p, lint q)
	{
		return (p + q - 1) / q;
	}

#if(__cplusplus < 201703L)

	lint gcd(lint a, lint b) {
		while (1) {
			if (a < b) swap(a, b);
			if (!b) break;
			a %= b;
		}
		return a;
	}

	lint lcm(lint a, lint b)
	{
		return a / gcd(a, b) * b;
	}

#endif

	lint powInt(lint a, lint b)
	{
		if (b == 0)
		{
			return 1;
		}
		if (b == 1)
		{
			return a;
		}
		lint tmp = powInt(a, b / 2);
		return (b % 2 == 1 ? a * tmp * tmp : tmp * tmp);
	}

	template<class T>
	T sgn(T val)
	{
		if (val == T(0))
			return T(0);
		if (val < 0)
			return T(-1);
		if (val > 0)
			return T(1);
	}

	template<class T>
	constexpr auto modK_belowN(T k, T MOD, T n)
	{
		return (n + MOD - k - 1) / MOD;
	}

	template<class It, class T>
	bool exist(It begin, It end, const T& val)
	{
		return find(begin, end, val) != end;
	}

	template<class It, class Pr>
	bool exist_if(It begin, It end, Pr pred)
	{
		return find_if(begin, end, pred) != end;
	}

	template<class T>
	bool between(T val, T l, T r)
	{
		return (val >= l) && (val <= r);
	}

	template<class It>
	auto carr(It begin, It end) {
		vec c;
		c.push_back(1);
		auto before = *begin;
		for (auto it = begin + 1; it != end; it++) {
			if (before != *it) {
				c.push_back(0);
				before = *it;
			}
			c.back()++;
		}
		return c;
	}

	template<class T>
	struct nval {
		lint n;
		T val;
		nval() : n(0) {};
		nval(lint _n, T _val) : n(_n), val(_val) {};
	};

	template<class It>
	auto carr2(It begin, It end) {
		using T = nval<remove_reference_t<decltype(*begin)>>;

		vect<T> c;
		c.push_back(T(1, *begin));
		auto before = *begin;
		for (auto it = begin + 1; it != end; it++) {
			if (before != *it) {
				c.push_back(T(0, *it));
				before = *it;
			}
			c.back().n++;
		}
		return c;
	}

	template<class It, class ...T>
	void sort2(It begin, It end, T ...p)
	{
		using val_t = remove_reference_t<decltype(*begin)>;

		sort(begin, end, [p...](val_t a, val_t b) {
			bool neq[] = { (a.*p != b.*p)... };
			bool sg[] = { (a.*p < b.*p)... };

			rep(i, sizeof...(p)) {
				if (neq[i])
				{
					return sg[i];
				}
			}
			return false;
		});
	}

	template<size_t _K, size_t _N, class ...Types, size_t ...indices>
	auto constexpr __ModKtuple_Impl(index_sequence<indices...>, tuple<Types...> args)
	{
		return make_tuple(get<indices* _N + _K>(args)...);
	}

	template<size_t K, size_t N, class ...Types>
	auto constexpr ModKtuple(Types ...args)
	{
		return __ModKtuple_Impl<K, N>(make_index_sequence<modK_belowN(K, N, sizeof...(args))>{}, forward_as_tuple(args...));
	}

	template<class It, class ...T, class ...Tsg, size_t ...indices>
	void __sort3_Impl(It begin, It end, tuple<T...> p, tuple<Tsg...> sgf, index_sequence<indices...>)
	{
		using val_t = remove_reference_t<decltype(*begin)>;

		sort(begin, end, [p, sgf](val_t a, val_t b) {
			bool neq[] = { (a.*(get<indices>(p)) != b.*(get<indices>(p)))... };
			bool sg[] = { ((a.*(get<indices>(p)) < b.*(get<indices>(p))) != (get<indices>(sgf))) ... };

			rep(i, sizeof...(indices)) {
				if (neq[i])
				{
					return sg[i];
				}
			}
			return false;
			});
	}

	template<class It, class ...T>
	void sort3(It begin, It end, T ...p)
	{
		using val_t = remove_reference_t<decltype(*begin)>;

		auto p_forward = ModKtuple<0, 2>(p...);
		auto sgf_forward = ModKtuple<1, 2>(p...);

		constexpr auto p_sz = tuple_size<decltype(p_forward)>::value;
		constexpr auto sgf_sz = tuple_size<decltype(sgf_forward)>::value;

		static_assert(p_sz == sgf_sz, "arg err");

		__sort3_Impl(begin, end, p_forward, sgf_forward, make_index_sequence<p_sz>{});
	}

	template<class It, class It2>
	auto spacel(It i, It2 end)
	{
		if (i + 1 == end)
		{
			return '\n';
		}
		else
		{
			return ' ';
		}
	}

	bool match(string s, string r)
	{
		return regex_match(s, regex(r));
	}

	template<class It>
	bool next_comb(lint n, It begin, It end)
	{
		auto rend = make_reverse_iterator(begin);
		auto rbegin = make_reverse_iterator(end);

		auto rit = rbegin;
		for (; rit != rend; rit++)
		{
			if ((rit == rbegin && (*rit) + 1 != n) ||
				(rit != rbegin && (*rit) + 1 != *(rit - 1)))
			{
				goto found;
			}
		}
		return false;
	found:;
		(*rit)++;

		for (auto it = rit.base(); it != end; it++)
		{
			(*it) = (*(it - 1)) + 1;
		}
		return true;
	}

	ostream& setp(ostream& ost)
	{
		cout << setprecision(60) << fixed;
		return ost;
	}

#ifdef _LOCAL
	auto& dbg = cout;
#else
	struct dummy_cout
	{
		template<class T>
		dummy_cout& operator<<(T&& op)
		{
			return *this;
		}

		using endl_t = basic_ostream<char, char_traits<char>>;

		dummy_cout& operator<<(endl_t& (*)(endl_t&))
		{
			return *this;
		}
	};

	dummy_cout dbg;
#endif
};

lint n;
string s;

int main()
{
	cin >> n >> s;

	lint ans = 0;


	rep(i, 1000)
	{
		lint tmp = i;
		vec a(3);
		rep(j, 3)
		{
			a[j] = tmp % 10;
			tmp /= 10;
		}

		lint p = 0;
		rep(j, n)
		{
			if (s[j] == '0' + a[p])
			{
				p++;
			}
			if (p == 3)
			{
				break;
			}
		}
		ans += (p == 3);
	}

	cout << ans << endl;
	return 0;
}