#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename CostType>
struct Edge {
  int src, dst; CostType cost;
  Edge(int src, int dst, CostType cost = 0) : src(src), dst(dst), cost(cost) {}
  inline bool operator<(const Edge &x) const {
    return cost != x.cost ? cost < x.cost : dst != x.dst ? dst < x.dst : src < x.src;
  }
  inline bool operator<=(const Edge &x) const { return !(x < *this); }
  inline bool operator>(const Edge &x) const { return x < *this; }
  inline bool operator>=(const Edge &x) const { return !(*this < x); }
};

int main() {
  int n; string s; cin >> n >> s;
  int m = s.length();
  string t = s;
  reverse(ALL(t));
  vector<vector<Edge<char>>> graph(n);
  REP(_, n - 1) {
    int u, v; char c; cin >> u >> v >> c; --u; --v;
    graph[u].emplace_back(u, v, c);
    graph[v].emplace_back(v, u, c);
  }
  int ans = 0;
  vector dp1(n, vector(m + 1, 0)), dp2(n, vector(m + 1, 0));
  auto f = [&](auto &&f, int par, int ver) -> void {
    for (const Edge<char> &e : graph[ver]) {
      if (e.dst == par) continue;
      f(f, ver, e.dst);
      vector<int> child1(m + 1, -INF), child2(m + 1, -INF);
      REP(i, m + 1) {
        chmax(child1[i], dp1[e.dst][i]);
        chmax(child2[i], dp2[e.dst][i]);
        if (i + 1 <= m) {
          chmax(child1[i + 1], dp1[e.dst][i] + (e.cost == s[i]));
          chmax(child2[i + 1], dp2[e.dst][i] + (e.cost == t[i]));
        }
      }
      REP(i, m + 1) {
        chmax(ans, dp1[ver][i] + child2[m - i]);
        chmax(ans, dp2[ver][i] + child1[m - i]);
        chmax(dp1[ver][i], child1[i]);
        chmax(dp2[ver][i], child2[i]);
      }
    }
  };
  f(f, -1, 0);
  cout << ans << '\n';
  return 0;
}