//@formatter:off
#include<bits/stdc++.h>

#include <utility>
#define overload4(_1,_2,_3,_4,name,...) name
#define rep1(i,n) for (ll i = 0; i < ll(n); ++i)
#define rep2(i,s,n) for (ll i = ll(s); i < ll(n); ++i)
#define rep3(i,s,n,d) for(ll i = ll(s); i < ll(n); i+=d)
#define rep(...) overload4(__VA_ARGS__,rep3,rep2,rep1)(__VA_ARGS__)
#define rrep1(i,n) for (ll i = ll(n)-1; i >= 0; i--)
#define rrep2(i,n,t) for (ll i = ll(n)-1; i >= (ll)t; i--)
#define rrep3(i,n,t,d) for (ll i = ll(n)-1; i >= (ll)t; i-=d)
#define rrep(...) overload4(__VA_ARGS__,rrep3,rrep2,rrep1)(__VA_ARGS__)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define popcount(x) __builtin_popcountll(x)
#define pb push_back
#define eb emplace_back
#ifdef __LOCAL
#define debug(...) { cout << #__VA_ARGS__; cout << ": "; print(__VA_ARGS__); cout << flush; }
#else
#define debug(...) void(0)
#endif
#define INT(...) int __VA_ARGS__;scan(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;scan(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;scan(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;scan(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;scan(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;scan(__VA_ARGS__)
using namespace std;
using ll = long long;
using ld = long double;
using P = pair<int,int>;
using LP = pair<ll,ll>;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vl = vector<ll>;
using vvl = vector<vector<ll>>;
using vd = vector<double>;
using vvd = vector<vector<double>>;
using vs = vector<string>;
using vc = vector<char>;
using vvc = vector<vector<char>>;
using vb = vector<bool>;
using vvb = vector<vector<bool>>;
using vp = vector<P>;
using vvp = vector<vector<P>>;
template<class S,class T> istream& operator>>(istream &is,pair<S,T> &p) { return is >> p.first >> p.second; }
template<class S,class T> ostream& operator<<(ostream &os,const pair<S,T> &p) { return os<<'{'<<p.first<<","<<p.second<<'}'; }
template<class T> istream& operator>>(istream &is,vector<T> &v) { for(T &t:v){is>>t;} return is; }
template<class T> ostream& operator<<(ostream &os,const vector<T> &v) { os<<'[';rep(i,v.size())os<<v[i]<<(i==int(v.size()-1)?"":","); return os<<']'; }
template<class T> void vecout(const vector<T> &v,char div='\n') { rep(i,v.size()) cout<<v[i]<<(i==int(v.size()-1)?'\n':div);}
template<class T> bool chmin(T& a,T b) {if(a > b){a = b; return true;} return false;}
template<class T> bool chmax(T& a,T b) {if(a < b){a = b; return true;} return false;}
void scan(){}
template <class Head, class... Tail> void scan(Head& head, Tail&... tail){ cin >> head; scan(tail...); }
template<class T> void print(const T& t){ cout << t << '\n'; }
template <class Head, class... Tail> void print(const Head& head, const Tail&... tail){ cout<<head<<' '; print(tail...); }
template<class... T> void fin(const T&... a) { print(a...); exit(0); }
struct Init_io {
    Init_io() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
        cout.tie(nullptr);
        cout << boolalpha << fixed << setprecision(15);
    }
} init_io;
const string yes[] = {"no","yes"};
const string Yes[] = {"No","Yes"};
const string YES[] = {"NO","YES"};
const int inf = 1001001001;
const ll linf = 1001001001001001001;
//@formatter:on

template<class T, T (*merge)(T, T), T (*add_root)(T, int, int), T (*id)()>
class rerooting {
    int n;
    vvi tree;
    vector<vector<T>> dp;
    vector<T> ans;
    
    T dfs(int u = 0, int p = -1) {
        T sum = id();
        dp[u].resize(tree[u].size());
        rep(i, tree[u].size()) {
            int v = tree[u][i];
            if (v == p) continue;
            dp[u][i] = dfs(v, u);
            sum = merge(sum, add_root(dp[u][i], u, v));
        }
        return sum;
    }
    
    void dfs2(T dpP, int u = 0, int p = -1) {
        int sz = tree[u].size();
        rep(i, sz) if (tree[u][i] == p) dp[u][i] = dpP;
        vector<T> sumL(sz + 1, id()), sumR(sz + 1, id());
        rep(i, sz) sumL[i + 1] = merge(sumL[i], add_root(dp[u][i], u, tree[u][i]));
        rrep(i, sz) sumR[i] = merge(sumR[i + 1], add_root(dp[u][i], u, tree[u][i]));
        ans[u] = sumL[sz];
        rep(i, sz) {
            int v = tree[u][i];
            if (v == p) continue;
            T t = merge(sumL[i], sumR[i + 1]);
            dfs2(t, v, u);
        }
    }

public:
    explicit rerooting(const vvi &tree) : n(tree.size()), tree(tree), dp(n), ans(n) {
        dfs();
        dfs2(id());
    };
    
    T get_ans(int i) {
        return ans[i];
    }
};

string s;
int m;
vvc ch;

vi merge(vi a, vi b) {
    vi res(m + 1);
    rep(i, m + 1) res[i] = max(a[i], b[i]);
    return move(res);
}

vi add_root(vi a, int u, int v) {
    char c = ch[u][v];
    vi res = a;
    rrep(i, m) {
        chmax(res[i], res[i + 1]);
        if (s[i] == c) chmax(res[i], a[i + 1] + 1);
    }
    return move(res);
}

vi id() {
    return vi(m + 1, 0);
}

int main() {
    INT(n);
    scan(s);
    m = s.size();
    ch.resize(n);
    rep(i, n) ch[i].resize(n);
    vvi G(n);
    rep(_, n - 1) {
        INT(u, v);
        CHR(c);
        u--, v--;
        G[u].pb(v);
        G[v].pb(u);
        ch[u][v] = ch[v][u] = c;
    }
    rerooting<vi, merge, add_root, id> rt(G);
    int ans = 0;
    rep(i, n) chmax(ans, rt.get_ans(i)[0]);
    fin(ans);
}