#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <bitset>
#include <fstream>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define x first
#define y second
#define Time (double)clock()/CLOCKS_PER_SEC
#define debug(x) std::cerr << #x << ": " << x << '\n';
#define FOR(i, n) for (int i = 0; i < n; ++i)
#define FORN(i, n) for (int i = 1; i <= n; ++i)
#define pb push_back
#define trav(a, x) for (auto& a : x)
using vi = vector<int>;
template <typename T>
std::istream& operator >>(std::istream& input, std::vector<T>& data)
{
    for (T& x : data)
        input >> x;
    return input;
}
template <typename T>
std::ostream& operator <<(std::ostream& output, const pair <T, T> & data)
{
    output << "(" << data.x << "," << data.y << ")";
    return output;
}
template <typename T>
std::ostream& operator <<(std::ostream& output, const std::vector<T>& data)
{
    for (const T& x : data)
        output << x << " ";
    return output;
}
ll div_up(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll div_down(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down 
ll math_mod(ll a, ll b) { return a - b * div_down(a, b); }
#define tcT template<class T
#define tcTU tcT, class U
tcT> using V = vector<T>; 
tcT> void re(V<T>& x) { 
    trav(a, x)
        cin >> a;
}
tcT> bool ckmin(T& a, const T& b) {
    return b < a ? a = b, 1 : 0; 
} // set a = min(a,b)
tcT> bool ckmax(T& a, const T& b) {
    return a < b ? a = b, 1 : 0; 
}
ll gcd(ll a, ll b) {
    while (b) {
        tie(a, b) = mp(b, a % b);
    }
    return a;
}
const int N = 2007;
int pref[N][N], suf[N][N];

int n, len;
string s;
V <pair <int, char> > g[N];
int ans = 0;
void dfs(int u, int p, char c) {
    trav (e, g[u]) {
        int v = e.x;
        char go = e.y;
        if (v != p) {
            dfs(v, u, go);

            FOR (i, len + 1) {
                ckmax(ans, pref[u][i] + suf[v][len - i]);
                ckmax(ans, pref[v][i] + suf[u][len - i]);
            }

            FOR (i, len + 1) {
                ckmax(pref[u][i], pref[v][i]);
                ckmax(suf[u][i], suf[v][i]);
            }
        }
    }
    if (u != 1) {
        for (int i = len - 1; i >= 0; --i) {
            if (s[i] == c) {
                ckmax(pref[u][i + 1], pref[u][i] + 1);
            }
        }
        FOR (i, len) {
            ckmax(pref[u][i + 1], pref[u][i]);
        }

        for (int i = len - 1; i >= 0; --i) {
            int p = len - 1 - i;
            if (s[p] == c) {
                ckmax(suf[u][i + 1], suf[u][i] + 1);
            }
        }
        FOR (i, len) {
            ckmax(suf[u][i + 1], suf[u][i]);
        }
    }
    FOR (i, len + 1) {
        ckmax(ans, pref[u][i]);
        ckmax(ans, suf[u][i]);
    }
}

signed main() {
    #ifdef LOCAL
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif
    cin >> n;
    cin >> s;
    len = s.size();
    FOR (i, n - 1) {
        int u, v;
        char c;
        cin >> u >> v >> c;
        g[u].app(mp(v, c));
        g[v].app(mp(u, c));
    }
    dfs(1, 1, 0);
    cout << ans << endl;
}