// >>> TEMPLATES
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
#define int ll
#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 repR(i, n) for (int i = (int)(n)-1; i >= 0; i--)
#define rep1R(i, n) for (int i = (int)(n); i >= 1; i--)
#define loop(i, a, B) for (int i = a; i B; i++)
#define loopR(i, a, B) for (int i = a; i B; i--)
#define all(x) begin(x), end(x)
#define allR(x) rbegin(x), rend(x)
#define rng(x, l, r) begin(x) + (l), begin(x) + (r)
#define pb push_back
#define eb emplace_back
#define fst first
#define snd second
template <class A, class B> constexpr auto mp(A &&a, B &&b) { return make_pair(forward<A>(a), forward<B>(b)); }
template <class... T> constexpr auto mt(T&&... x) { return make_tuple(forward<T>(x)...); }
template <class Int> auto constexpr inf_ = numeric_limits<Int>::max()/2-1;
auto constexpr INF32 = inf_<int32_t>;
auto constexpr INF64 = inf_<int64_t>;
auto constexpr INF   = inf_<int>;
#ifdef LOCAL
#include "debug.hpp"
#else
#define dump(...) (void)(0)
#define say(x) (void)(0)
#define debug if (0)
#endif
template <class T, class Comp> struct pque : priority_queue<T, vector<T>, Comp> { vector<T> &data() { return this->c; } void clear() { this->c.clear(); } };
template <class T> using pque_max = pque<T, less<T>>;
template <class T> using pque_min = pque<T, greater<T>>;
template <class T, class = typename T::iterator, enable_if_t<!is_same<T, string>::value, int> = 0>
ostream& operator<<(ostream& os, T const& a) { bool f = true; for (auto const& x : a) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, size_t N, enable_if_t<!is_same<T, char>::value, int> = 0>
ostream& operator<<(ostream& os, const T (&a)[N]) { bool f = true; for (auto const& x : a) os << (f ? "" : " ") << x, f = false; return os; }
template <class T, class = decltype(begin(declval<T&>())), class = typename enable_if<!is_same<T, string>::value>::type>
istream& operator>>(istream& is, T &a) { for (auto& x : a) is >> x; return is; }
template <class T, class S> ostream& operator<<(ostream& os, pair<T, S> const& p) { return os << p.first << " " << p.second; }
template <class T, class S> istream& operator>>(istream& is, pair<T, S>& p) { return is >> p.first >> p.second; }
struct IOSetup { IOSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); } } iosetup;
template <class F> struct FixPoint : private F {
    constexpr FixPoint(F&& f) : F(forward<F>(f)) {}
    template <class... T> constexpr auto operator()(T&&... x) const { return F::operator()(*this, forward<T>(x)...); }
};
struct MakeFixPoint { template <class F> constexpr auto operator|(F&& f) const { return FixPoint<F>(forward<F>(f)); } };
#define MFP MakeFixPoint()|
#define def(name, ...) auto name = MFP [&](auto &&name, __VA_ARGS__)
template <class T, size_t d> struct vec_impl {
    using type = vector<typename vec_impl<T, d-1>::type>;
    template <class... U> static type make_v(size_t n, U&&... x) { return type(n, vec_impl<T, d-1>::make_v(forward<U>(x)...)); }
};
template <class T> struct vec_impl<T, 0> { using type = T; static type make_v(T const& x = {}) { return x; } };
template <class T, size_t d = 1> using vec = typename vec_impl<T, d>::type;
template <class T, size_t d = 1, class... Args> auto make_v(Args&&... args) { return vec_impl<T, d>::make_v(forward<Args>(args)...); }
template <class T> void quit(T const& x) { cout << x << endl; exit(0); }
template <class T, class U> constexpr bool chmin(T& x, U const& y) { if (x > y) { x = y; return true; } return false; }
template <class T, class U> constexpr bool chmax(T& x, U const& y) { if (x < y) { x = y; return true; } return false; }
template <class It> constexpr auto sumof(It b, It e) { return accumulate(b, e, typename iterator_traits<It>::value_type{}); }
template <class T> int sz(T const& x) { return x.size(); }
template <class C, class T> int lbd(C const& v, T const& x) { return lower_bound(begin(v), end(v), x)-begin(v); }
template <class C, class T> int ubd(C const& v, T const& x) { return upper_bound(begin(v), end(v), x)-begin(v); }
constexpr int64_t mod(int64_t x, int64_t m) { assert(m > 0); return (x %= m) < 0 ? x+m : x; }
constexpr int64_t div_floor(int64_t x, int64_t y) { assert(y != 0); return x/y - ((x^y) < 0 and x%y); }
constexpr int64_t div_ceil(int64_t x, int64_t y) { assert(y != 0); return x/y + ((x^y) > 0 and x%y); }
constexpr int dx[] = { 1, 0, -1, 0, 1, -1, -1, 1 };
constexpr int dy[] = { 0, 1, 0, -1, 1, 1, -1, -1 };
constexpr int popcnt(ll x) { return __builtin_popcountll(x); }
mt19937_64 seed_{random_device{}()};
template <class Int> Int rand(Int a, Int b) { return uniform_int_distribution<Int>(a, b)(seed_); }
i64 irand(i64 a, i64 b) { return rand<i64>(a, b); } // [a, b]
u64 urand(u64 a, u64 b) { return rand<u64>(a, b); } //
template <class It> void shuffle(It l, It r) { shuffle(l, r, seed_); }
vector<int> &operator--(vector<int> &v) { for (int &x : v) --x; return v; }
vector<int> &operator++(vector<int> &v) { for (int &x : v) ++x; return v; }
// <<<
// >>> re-rooting
// >>> edge info
#ifndef EDGE_INFO
#define EDGE_INFO
constexpr int dest(int v) { return v; }
template <class E, class = decltype(declval<E>().to)>
constexpr int dest(E const& e) { return e.to; }
constexpr int cost(int) { return 1; }
template <class E, class = decltype(declval<E>().cost)>
constexpr auto cost(E const& e) { return e.cost; }
template <class E> using cost_t = decltype(cost(declval<E>()));
#endif
// <<<
template <class Edge, class Monoid, class Merge, class AddEdge, class AddVertex>
struct ReRooting {
    vector<vector<Edge>> const* g;
    Monoid unit;
    Merge merge; // (Monoid, Monoid) -> Monoid
    AddEdge lift; // (Monoid, Edge) -> Monoid
    AddVertex add_vertex; // (Monoid, int vertex) -> Monoid
    vector<Monoid> dp_sub, dp_par, dp_all;
    ReRooting(vector<vector<Edge>> const& g, Monoid unit, Merge merge, AddEdge lift, AddVertex add_vertex)
        : g(&g), unit(unit), merge(merge), lift(lift), add_vertex(add_vertex),
          dp_sub(g.size(), unit), dp_par(g.size(), unit), dp_all(g.size(), unit) {}
    vector<Monoid> run() {
        assert(g->size());
        dfs1(0, -1);
        dfs2(0, -1);
        dump(dp_sub); // lifted
        dump(dp_par); // lifted
        dump(dp_all);
        return dp_all;
    }
    void dfs1(int x, int p) {
        Monoid val = unit;
        for (auto const& e : (*g)[x]) {
            const int y = dest(e);
            if (y == p) continue;
            dfs1(y, x);
            val = merge(val, lift(dp_sub[y], e));
        }
        dp_sub[x] = add_vertex(val, x);
    }
    void dfs2(int x, int p) {
        auto const& es = (*g)[x];
        auto d = [&](int i) { return dest(es[i]); };
        auto val = [&](int i) -> Monoid& { return d(i) == p ? dp_par[x] : dp_sub[d(i)]; };
        const int m = es.size();
        for (int i = 0; i < m; ++i) val(i) = lift(val(i), es[i]);
        {
            vector<Monoid> ldp(m+1, unit), rdp(m+1, unit);
            for (int i = 0; i < m; i++) ldp[i+1] = merge(ldp[i], val(i));
            for (int i = m-1; i >= 0; i--) rdp[i] = merge(rdp[i+1], val(i));
            dp_all[x] = add_vertex(rdp[0], x);
            for (int i = 0; i < m; i++) {
                if (d(i) == p) continue;
                dp_par[d(i)] = add_vertex(merge(ldp[i], rdp[i+1]), x);
            }
        }
        for (int i = 0; i < m; i++) if (d(i) != p) dfs2(d(i), x);
    }
};
// <<<

int32_t main() {
    int n; cin >> n;
    string s; cin >> s;
    struct edge { int to; char c; };
    vector<vector<edge>> g(n);
    rep (i, n-1) {
        int x, y; cin >> x >> y; --x, --y;
        char c; cin >> c;
        g[x].pb({y, c});
        g[y].pb({x, c});
    }

    vector<int> unit(s.size() + 1);
    auto merge = [&](vector<int> a, vector<int> const& b) {
        rep (i, a.size()) chmax(a[i], b[i]);
        return a;
    };
    auto lift = [&](vector<int> const& a, edge const& e) {
        vector<int> ret(s.size() + 1);
        repR (i, s.size()) {
            if (s[i] == e.c) chmax(ret[i], a[i+1] + 1);
            chmax(ret[i], a[i]);
            chmax(ret[i], ret[i+1]);
        }
        return ret;
    };
    auto add_vertex = [&](vector<int> const& a, int) { return a; };
    auto rr = ReRooting(g, unit, merge, lift, add_vertex);
    auto dp = rr.run();

    int ma = 0;
    rep (i, dp.size()) chmax(ma, *max_element(all(dp[i])));
    cout << ma << '\n';
}