/**
 *    author:  otera
 *    created: 30.04.2021 22:44:11 
**/
#include<bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
using ull = unsigned long long;
using uint = unsigned;
const int inf=1e9+7;
const ll INF=1LL<<60;
#define repa(i, n) for(int i = 0; i < n; ++ i)
#define repb(i, a, b) for(int i = a; i < b; ++ i)
#define repc(i, a, b, c) for(int i = a; i < b; i += c)
#define overload4(a, b, c, d, e, ...) e
#define rep(...) overload4(__VA_ARGS__, repc, repb, repa)(__VA_ARGS__)
#define rep1a(i, n) for(int i = 0; i <= n; ++ i)
#define rep1b(i, a, b) for(int i = a; i <= b; ++ i)
#define rep1c(i, a, b, c) for(int i = a; i <= b; i += c)
#define rep1(...) overload4(__VA_ARGS__, rep1c, rep1b, rep1a)(__VA_ARGS__)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define per1(i,n) for(int i=n;i>=1;i--)
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
#define pb push_back
#define eb emplace_back
#define fr first
#define sc second
#define all(c) c.begin(),c.end()
#define lb(c, x) distance((c).begin(), lower_bound(all(c), (x)))
#define ub(c, x) distance((c).begin(), upper_bound(all(c), (x)))
#define Sort(a) sort(all(a))
#define Rev(a) reverse(all(a))
#define Uniq(a) sort(all(a));a.erase(unique(all(a)),end(a))
#define si(c) (int)(c).size()
inline ll popcnt(ull a){ return __builtin_popcountll(a); }
#define tpow(n) (1LL<<(n))
#define unless(A) if(!(A))
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll intpow(ll a, ll b, ll m) {ll ans = 1; while(b){ if(b & 1) (ans *= a) %= m; (a *= a) %= m; b /= 2; } return ans; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define ULL(...) ull __VA_ARGS__;in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;in(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;in(__VA_ARGS__)
#define vec(type,name,...) vector<type>name(__VA_ARGS__)
#define VEC(type,name,size) vector<type>name(size);in(name)
#define vv(type,name,h,...) vector<vector<type>>name(h,vector<type>(__VA_ARGS__))
#define VV(type,name,h,w) vector<vector<type>>name(h,vector<type>(w));in(name)
#define vvv(type,name,h,w,...) vector<vector<vector<type>>>name(h,vector<vector<type>>(w,vector<type>(__VA_ARGS__)))
template <class T> using vc = vector<T>;
template <class T> using vvc = vector<vc<T>>;
template <class T> using vvvc = vector<vvc<T>>;
template <class T> using vvvvc = vector<vvvc<T>>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqg = priority_queue<T, vector<T>, greater<T>>;
template<class T> void scan(T& a){ cin >> a; }
template<class T> void scan(vector<T>& a){ for(auto&& i : a) scan(i); }
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail){ scan(head); in(tail...); }
void print(){ cout << ' '; }
template<class T> void print(const T& a){ cout << a; }
template<class T> void print(const vector<T>& a){ if(a.empty()) return; print(a[0]); for(auto i = a.begin(); ++i != a.end(); ){ cout << ' '; print(*i); } }
int out(){ cout << '\n'; return 0; }
template<class T> int out(const T& t){ print(t); cout << '\n'; return 0; }
template<class Head, class... Tail> int out(const Head& head, const Tail&... tail){ print(head); cout << ' '; out(tail...); return 0; }
#define CHOOSE(a) CHOOSE2 a
#define CHOOSE2(a0,a1,a2,a3,a4,x,...) x
#define debug_1(x1) cout<<#x1<<": "<<x1<<endl
#define debug_2(x1,x2) cout<<#x1<<": "<<x1<<", "#x2<<": "<<x2<<endl
#define debug_3(x1,x2,x3) cout<<#x1<<": "<<x1<<", "#x2<<": "<<x2<<", "#x3<<": "<<x3<<endl
#define debug_4(x1,x2,x3,x4) cout<<#x1<<": "<<x1<<", "#x2<<": "<<x2<<", "#x3<<": "<<x3<<", "#x4<<": "<<x4<<endl
#define debug_5(x1,x2,x3,x4,x5) cout<<#x1<<": "<<x1<<", "#x2<<": "<<x2<<", "#x3<<": "<<x3<<", "#x4<<": "<<x4<<", "#x5<<": "<<x5<<endl
#ifdef DEBUG
#define debug(...) CHOOSE((__VA_ARGS__,debug_5,debug_4,debug_3,debug_2,debug_1,~))(__VA_ARGS__)
#define dump(...) { print(#__VA_ARGS__); print(":"); out(__VA_ARGS__); }
#else
#define debug(...)
#define dump(...)
#endif

typedef pair<int, char> P2;

void solve() {
    INT(n);
    STR(s);
    string rs = s;
    Rev(rs);
    vvc<P2> g(n);
    rep(i, n - 1) {
        INT(u, v); -- u, -- v; 
        CHR(c);
        g[u].eb(v, c);
        g[v].eb(u, c);
    }
    int sz = si(s);
    vvc<int> dp(n, vc<int>(sz + 1, 0)), rdp(n, vc<int>(sz + 1, 0));
    int ans = 0;
    auto dfs = [&](auto&& self, int v, int p) -> void {
        for(auto e: g[v]) {
            int nv = e.fr; char c = e.sc;
            if(nv == p) continue;
            self(self, nv, v);
            rep(j, sz + 1) {
                chmax(ans, dp[v][j] + rdp[nv][sz - j]);
                chmax(ans, rdp[v][j] + dp[nv][sz - j]);
                if(j < sz) {
                    if(s[j] == c) {
                        chmax(ans, dp[nv][j] + 1 + rdp[v][sz - 1 - j]);
                    }
                    if(rs[j] == c) {
                        chmax(ans, rdp[nv][j] + 1 + dp[v][sz - 1 - j]);
                    }
                }
            }
            rep(i, sz + 1) {
                chmax(dp[v][i], dp[nv][i]);
                chmax(rdp[v][i], rdp[nv][i]);
                if(i < sz and s[i] == c) {
                    chmax(dp[v][i + 1], dp[nv][i] + 1);
                }
                if(i < sz and rs[i] == c) {
                    chmax(rdp[v][i + 1], rdp[nv][i] + 1);
                }
            }
            rep(i, sz) {
                chmax(dp[v][i + 1], dp[v][i]);
                chmax(rdp[v][i + 1], rdp[v][i]);
            }
        }
    };
    dfs(dfs, 0, -1);
    rep(i, n) {
        chmax(ans, dp[i][sz]);
        chmax(ans, rdp[i][sz]);
    }
    out(ans);
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    // cout << fixed << setprecision(20);
    // INT(t); rep(i, t)solve();
    solve();
    return 0;
}