#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i = 0; i < n; i++)
#define rep2(i, x, n) for(int i = x; i <= n; i++)
#define rep3(i, x, n) for(int i = x; i >= n; i--)
#define each(e, v) for(auto &e: v)
#define pb push_back
#define eb emplace_back
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) (int)x.size()
using ll = long long;
using pii = pair<int, int>;
using pil = pair<int, ll>;
using pli = pair<ll, int>;
using pll = pair<ll, ll>;
const int MOD = 1000000007;
//const int MOD = 998244353;
const int inf = (1<<30)-1;
const ll INF = (1LL<<60)-1;
template<typename T> bool chmax(T &x, const T &y) {return (x < y)? (x = y, true) : false;};
template<typename T> bool chmin(T &x, const T &y) {return (x > y)? (x = y, true) : false;};

struct io_setup{
    io_setup(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout << fixed << setprecision(15);
    }
} io_setup;

vector<string> S(2);
int N, M;
vector<vector<vector<int>>> dp(2, vector<vector<int>>(2000, vector<int>(2001, 0)));
int ans = 0;

template<typename T, bool directed = false>
struct Weighted_Graph{
    struct edge{
        int to; T cost; int id;
        edge(int to, T cost, int id) : to(to), cost(cost), id(id) {}
    };

    vector<vector<edge>> es;
    const T INF_T;
    const int n;
    int m;

    Weighted_Graph(int n) : es(n), INF_T(numeric_limits<T>::max()/2), n(n), m(0) {}

    void add_edge(int from, int to, T cost){
        es[from].emplace_back(to, cost, m);
        if(!directed) es[to].emplace_back(from, cost, m);
        m++;
    }

    void dfs(int now, int pre = -1){
        each(e, es[now]){
            if(e.to != pre) dfs(e.to, now);
        }

        vector<vector<int>> L(M+1), R(M+1), C(M+1);

        rep(t, 2){
            rep2(i, 0, M){
                int k = 0;
                each(e, es[now]){
                    if(e.to == pre) continue;

                    int tmp = dp[t][e.to][i];
                    if(i > 0){
                        if(t == 0) chmax(tmp, C[i-1][k]);
                        else chmax(tmp, L[i-1][k]);
                    }
                    if(i > 0 && S[t][M-i] == e.cost){
                        chmax(tmp, dp[t][e.to][i-1]+1);
                    }

                    if(t == 0) C[i].eb(tmp);
                    else L[i].eb(tmp), R[i].eb(tmp);

                    chmax(dp[t][now][i], tmp);
                    k++;
                }

                if(i > 0) chmax(dp[t][now][i], dp[t][now][i-1]);
            }
        }

        int K = sz(L[0]);

        rep2(i, 0, M){
            rep2(j, 1, K-1){
                chmax(L[i][j], L[i][j-1]);
            }
            rep3(j, K-2, 0){
                chmax(R[i][j], R[i][j+1]);
            }
        }

        chmax(ans, dp[0][now][M]), chmax(ans, dp[1][now][M]);

        rep2(i, 0, M){
            rep(j, K){
                int x = 0;
                if(j-1 >= 0) chmax(x, L[i][j-1]);
                if(j+1 < K) chmax(x, R[i][j+1]);
                chmax(ans, C[M-i][j]+x);
            }
        }
    }

    void solve(){
        dfs(0);

        cout << ans << '\n';
        /*
        rep(i, N){
            rep(j, M+1){
                cout << dp[0][i][j] << ' ';
            }
            cout << '\n';
        }
        */
    }
};

int main(){
    cin >> N >> S[0];

    S[1] = S[0];
    reverse(all(S[1]));
    M = sz(S[0]);

    Weighted_Graph<char> G(N);

    rep(i, N-1){
        int u, v; char c; cin >> u >> v >> c; u--, v--;
        G.add_edge(u, v, c);
    }

    G.solve();
}