#pragma GCC target("avx2")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
#define DEBUG
#ifdef DEBUG
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template <class T> ostream &operator<<(ostream &os, const vector<T> &v) {
    os << '{';
    for(int i = 0; i < (int)v.size(); i++) {
        if(i) { os << ','; }
        os << v[i];
    }
    os << '}';
    return os;
}
void debugg() { cerr << endl; }
template <class T, class... Args>
void debugg(const T &x, const Args &... args) {
    cerr << " " << x;
    debugg(args...);
}
#define debug(...)                                                             \
    cerr << __LINE__ << " [" << #__VA_ARGS__ << "]: ", debugg(__VA_ARGS__)
#define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl
#else
#define debug(...) (void(0))
#define dump(x) (void(0))
#endif
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = (1<<30) - 1;
const ll linf = 1LL<<61;
const int MAX = 510000;
int dy[8] = {0,1,0,-1,1,-1,-1,1};
int dx[8] = {-1,0,1,0,1,-1,1,-1};
const double pi = 3.14159265358979;
const double eps = 1e-8;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<=b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    int sz = a.size();
    for(auto itr = a.begin(); itr != a.end(); itr++){
		cout << *itr;
        sz--;
        if(sz) cout << " ";
	}
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){
	cout << a << " " << b << "\n";
}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
void mark() {cout << "#" << "\n";}
ll pcount(ll x) {return __builtin_popcountll(x);}
const int mod = 1e9 + 7;
//const int mod = 998244353;

int dp[2020][2020];
int ep[2020][2020];

int main(){
    int n; cin >> n;
    string s; cin >> s;
    vector<vector<pair<int,char>>> G(n);
    rep(i,n-1){
        int u,v;
        char c;
        cin >> u >> v >> c; u--; v--;
        G[u].emplace_back(v,c);
        G[v].emplace_back(u,c);
    }
    int m = s.size();
    int ans = 0;
    auto dfs = [&](auto &&dfs, int u, int p) -> void {
        vector<pair<int,int>> d1(m+1,{0,-1}), d2(m+1,{0,-1}),e1(m+1,{0,-1}),e2(m+1,{0,-1});
        for(auto v : G[u]){
            if(v.first == p) continue;
            dfs(dfs,v.first,u);
            rep(i,m){
                int C = s[i] == v.second;
                if(dp[v.first][i] + C >= d1[i].first){
                    d2[i] = d1[i];
                    d1[i] = {dp[v.first][i] + C, v.first};
                }else if(dp[v.first][i] + C >= d2[i].first){
                    d2[i] = {dp[v.first][i] + C, v.first};
                }
                chmax(dp[u][i+1], dp[v.first][i] + C);
                chmax(ep[u][i], ep[v.first][i+1] + C);
            }
            for(int i=1; i<=m; i++){
                int C = s[i-1] == v.second;
                if(ep[v.first][i] + C >= e2[i].first){
                    e2[i] = e1[i];
                    e1[i] = {ep[v.first][i] + C, v.first};
                }else if(ep[v.first][i] + C >= e2[i].first){
                    e2[i] = {ep[v.first][i] + C, v.first};
                }
            }
        }
        for(auto v : G[u]){
            if(v.first == p) continue;
            rep(i,m){
                if(e1[i+1].second == v.first) chmax(ans, dp[v.first][i] + e2[i+1].first);
                else chmax(ans, dp[v.first][i] + e1[i+1].first);
                if(d1[i].second == v.first) chmax(ans, d2[i].first + ep[v.first][i+1]);
                else chmax(ans, d1[i].first + ep[v.first][i+1]);
            }
        }
        chmax(ans, dp[u][m]);
        chmax(ans, ep[u][0]);
        rep(i,m) chmax(dp[u][i+1], dp[u][i]);
        for(int i=m-1; i>=0; i--) chmax(ep[u][i], ep[u][i+1]);
    };
    dfs(dfs,0,-1);
    cout << ans << endl;
}