#include "bits/stdc++.h"
#include <random>
#include <chrono>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define SZ(x) ((lint)(x).size())
#define FOR(i, begin, end) for(lint i=(begin),i##_end_=(end);i<i##_end_;++i)
#define IFOR(i, begin, end) for(lint i=(end)-1,i##_begin_=(begin);i>=i##_begin_;--i)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define endk '\n'
using namespace std; typedef unsigned long long _ulong; typedef int lint; typedef long double ld; typedef pair<lint, lint> plint; typedef pair<ld, ld> pld;
struct fast_ios { fast_ios() { cin.tie(nullptr), ios::sync_with_stdio(false), cout << fixed << setprecision(20); }; } fast_ios_;
template<class T> auto add = [](T a, T b) -> T { return a + b; };
template<class T> auto f_max = [](T a, T b) -> T { return max(a, b); };
template<class T> auto f_min = [](T a, T b) -> T { return min(a, b); };
template<class T> using V = vector<T>;
using Vl = V<lint>; using VVl = V<Vl>;
template< typename T > ostream& operator<<(ostream& os, const vector< T >& v) {
	for (int i = 0; i < (int)v.size(); i++) os << v[i] << (i + 1 != v.size() ? " " : "");
	return os;
}
template< typename T >istream& operator>>(istream& is, vector< T >& v) {
	for (T& in : v) is >> in;
	return is;
}
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
template <class T>
T div_floor(T a, T b) {
	if (b < 0) a *= -1, b *= -1;
	return a >= 0 ? a / b : (a + 1) / b - 1;
}
template <class T>
T div_ceil(T a, T b) {
	if (b < 0) a *= -1, b *= -1;
	return a > 0 ? (a - 1) / b + 1 : a / b;
}
template <class F> struct rec {
	F f;
	rec(F&& f_) : f(std::forward<F>(f_)) {}
	template <class... Args> auto operator()(Args &&... args) const {
		return f(*this, std::forward<Args>(args)...);
	}
};
lint gcd(lint a, lint b) { if (b == 0) return a; else return gcd(b, a % b); }
lint digit(lint a) { return (lint)log10(a); }
lint e_dist(plint a, plint b) { return abs(a.first - b.first) * abs(a.first - b.first) + abs(a.second - b.second) * abs(a.second - b.second); }
lint m_dist(plint a, plint b) { return abs(a.first - b.first) + abs(a.second - b.second); }
bool check_overflow(lint a, lint b, lint limit) { if (b == 0) return false; return a > limit / b; } // a * b > c => true
void Worshall_Floyd(VVl& g) { REP(k, SZ(g)) REP(i, SZ(g)) REP(j, SZ(g)) chmin(g[i][j], g[i][k] + g[k][j]); }
const lint MOD1000000007 = 1000000007, MOD998244353 = 998244353, INF = 1e9;
lint dx[8] = { 0, -1, 0, 1, 1, -1, 1, -1 }, dy[8] = { -1, 0, 1, 0, -1, -1, 1, 1 };
bool YN(bool flag) { cout << (flag ? "YES" : "NO") << endk; return flag; } bool yn(bool flag) { cout << (flag ? "Yes" : "No") << endk; return flag; }
struct Edge {
	lint from, to;
	lint cost;
	Edge() {

	}
	Edge(lint u, lint v, lint c) {
		cost = c;
		from = u;
		to = v;
	}
	bool operator<(const Edge& e) const {
		return cost < e.cost;
	}
};
struct WeightedEdge {
	lint to;
	lint cost;
	WeightedEdge(lint v, lint c = 1) {
		to = v;
		cost = c;
	}
	bool operator<(const WeightedEdge& e) const {
		return cost < e.cost;
	}
};
using WeightedGraph = V<V<WeightedEdge>>;
typedef pair<lint, plint> tlint;
typedef pair<plint, plint> qlint;
typedef pair<lint, char> valstr;

lint N;
int main() {
	cin >> N;
	string s;
	cin >> s;
	VVl poses(26);
	REP(i, SZ(s)) poses[s[i] - 'a'].push_back(i);

	V<V<valstr>> to(N);
	REP(i, N - 1) {
		lint u, v;
		char c;
		cin >> u >> v >> c; u--; v--;
		to[u].push_back({ v, c });
		to[v].push_back({ u, c });
	}

	V<VVl> dp(N);
	Vl tmp(SZ(s) + 1, -1);
	V<map<lint, lint>> fx(N);
	REP(i, N) {
		dp[i].assign(SZ(to[i]), tmp);
		REP(j, SZ(to[i])) {
			fx[i][to[i][j].first] = j;
		}
	}

	auto dfs = [&](auto&& dfs, lint curr, lint prv, lint idx) -> lint {
		if (dp[curr][fx[curr][prv]][idx] != -1) return dp[curr][fx[curr][prv]][idx];
		lint maxv = 0;
		for (auto nxt : to[curr]) {
			if (prv == nxt.first) continue;
			lint _c = nxt.second - 'a';
			lint nxt_idx = lower_bound(ALL(poses[_c]), idx) - poses[_c].begin();
			if (nxt_idx != SZ(poses[_c])) {
				chmax(maxv, dfs(dfs, nxt.first, curr, poses[_c][nxt_idx] + 1) + 1);
			}
			else {
				chmax(maxv, dfs(dfs, nxt.first, curr, idx));
			}
		}
		return dp[curr][fx[curr][prv]][idx] = maxv;
	};

	lint ans = 0;
	REP(i, N) {
		chmax(ans, dfs(dfs, i, -1, -1));
	}
	cout << ans << endk;
}