#include <bits/stdc++.h>
using namespace std;
int main(){
  int N;
  cin >> N;
  string S;
  cin >> S;
  int M = S.size();
  vector<vector<pair<char, int>>> E(N);
  for (int i = 0; i < N - 1; i++){
    int u, v;
    char c;
    cin >> u >> v >> c;
    u--;
    v--;
    E[u].push_back(make_pair(c, v));
    E[v].push_back(make_pair(c, u));
  }
  vector<int> p(N, -1);
  vector<char> p2(N);
  vector<vector<int>> c(N);
  queue<int> Q;
  Q.push(0);
  vector<int> bfs;
  while (!Q.empty()){
    int v = Q.front();
    Q.pop();
    bfs.push_back(v);
    for (auto P : E[v]){
      int w = P.second;
      if (w != p[v]){
        p[w] = v;
        p2[w] = P.first;
        c[v].push_back(w);
        Q.push(w);
      }
    }
  }
  reverse(bfs.begin(), bfs.end());
  vector<vector<int>> dp1(N, vector<int>(M + 1, 0));
  for (int v : bfs){
    for (int w : c[v]){
      for (int i = 0; i <= M; i++){
        dp1[v][i] = max(dp1[v][i], dp1[w][i]);
      }
    }
    for (int i = 0; i < M; i++){
      dp1[v][i + 1] = max(dp1[v][i + 1], dp1[v][i]);
    }
    if (v != 0){
      for (int i = M - 1; i >= 0; i--){
        if (S[i] == p2[v]){
          dp1[v][i + 1] = max(dp1[v][i + 1], dp1[v][i] + 1);
        }
      }
    }
    for (int i = 0; i < M; i++){
      dp1[v][i + 1] = max(dp1[v][i + 1], dp1[v][i]);
    }
  }
  vector<vector<int>> dp2(N, vector<int>(M + 1, 0));
  for (int v : bfs){
    for (int w : c[v]){
      for (int i = M; i >= 0; i--){
        dp2[v][i] = max(dp2[v][i], dp2[w][i]);
      }
    }
    for (int i = M - 1; i >= 0; i--){
      dp2[v][i] = max(dp2[v][i], dp2[v][i + 1]);
    }
    if (v != 0){
      for (int i = 0; i < M; i++){
        if (S[i] == p2[v]){
          dp2[v][i] = max(dp2[v][i], dp2[v][i + 1] + 1);
        }
      }
    }
    for (int i = M - 1; i >= 0; i--){
      dp2[v][i] = max(dp2[v][i], dp2[v][i + 1]);
    }
  }
  int ans = 0;
  for (int v : bfs){
    vector<int> mx1(M + 1, 0);
    vector<int> mx2(M + 1, 0);
    for (int w : c[v]){
      for (int i = 0; i <= M; i++){
        ans = max(ans, mx1[i] + dp2[w][i]);
        mx1[i] = max(mx1[i], dp1[w][i]);
        ans = max(ans, mx2[i] + dp1[w][i]);
        mx2[i] = max(mx2[i], dp2[w][i]);
      }
    }
  }
  cout << ans << endl;
}