#include "bits/stdc++.h"
//#include "atcoder/all"
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

struct Edge {
	int to;
	char c;
	Edge(int _to, char _c) :to(_to), c(_c) {}
};
int n; string s;
vector<Edge>g[200005];
long long dp[2005][2005];//頂点i,Sの頭j文字目まで
long long dpr[2005][2005];//頂点i,Sの頭j文字から
long long ans;
void dfs(int v, int p = -1) {
	for (Edge e : g[v]) {
		if (p == e.to) continue;
		dfs(e.to, v);
		rrep2(i, 1, s.size() + 1) {
			chmax(dp[e.to][i], dp[e.to][i - 1] + (s[i - 1] == e.c));
		}
		rep2(i, 1, s.size() + 1) {
			chmax(dp[e.to][i], dp[e.to][i - 1]);
		}
		rep2(i, 1, s.size() + 1) {
			chmax(dpr[e.to][i - 1], dpr[e.to][i] + (s[i - 1] == e.c));
		}
		rrep2(i, 1, s.size() + 1) {
			chmax(dpr[e.to][i - 1], dpr[e.to][i]);
		}
		rep(i, s.size() + 1) {
			chmax(ans, dp[v][i] + dpr[e.to][i]);
			chmax(ans, dp[e.to][i] + dpr[v][i]);
		}
		rep(i, s.size() + 1) {
			chmax(dp[v][i], dp[e.to][i]);
			chmax(dpr[v][i], dpr[e.to][i]);
		}
	}
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin >> n >> s;
	rep(i, n - 1) {
		int u, v; cin >> u >> v;
		u--; v--;
		char c; cin >> c;
		g[u].emplace_back(v, c);
		g[v].emplace_back(u, c);
	}
	ans = 0;
	dfs(0);
	cout << ans << endl;
	return 0;
}