#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, t) for (int i = (int)(s); i < (int)(t); ++i)
#define revrep(i, t, s) for (int i = (int)(t)-1; i >= (int)(s); --i)
#define all(x) begin(x), end(x)
template <typename T>
bool chmax(T& a, const T& b) {
    return a < b ? (a = b, 1) : 0;
}
template <typename T>
bool chmin(T& a, const T& b) {
    return a > b ? (a = b, 1) : 0;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);

    int n;
    cin >> n;
    string w;
    cin >> w;
    vector<vector<int>> G(n);
    rep(i, 0, n - 1) {
        int u, v;
        cin >> u >> v;
        --u, --v;
        G[u].push_back(v);
        G[v].push_back(u);
    }
    if (w.size() == 1) {
        cout << n << endl;
        return 0;
    }
    if (w.size() == 2) {
        int ans = n - 1;
        if (w[0] == w[1]) {
            ans *= 2;
        }
        cout << ans << endl;
        return 0;
    }
    if (w[0] == w[2]) {
        vector<int> col(n, -1);
        auto dfs = [&](auto& dfs, int v) -> void {
            for (auto c : G[v]) {
                if (col[c] == -1) {
                    col[c] = col[v] ^ 1;
                    dfs(dfs, c);
                }
            }
        };
        col[0] = 0;
        dfs(dfs, 0);

        vector<ll> cnt(2);
        rep(i, 0, n) {
            ll d = G[i].size();
            cnt[col[i]] += d * (d - 1);
        }

        if (w[0] == w[1]) {
            cout << cnt[0] + cnt[1] << endl;
        } else {
            cout << max(cnt[0], cnt[1]) << endl;
        }
        return 0;
    }

    auto wr = w;
    reverse(all(wr));
    set<char> chars;
    for (auto c : w) chars.insert(c);

    vector<map<string, ll>> cnt(n), val(n);
    auto dfs = [&](auto& dfs, int v, int p) -> void {
        bool is_leaf = true;
        for (int c : G[v]) {
            if (c != p) {
                is_leaf = false;
                dfs(dfs, c, v);
            }
        }
        if (is_leaf) {
            for (auto c0 : chars) {
                string c01 = string(1, c0) + "?";
                cnt[v][c01] = 1;
            }
            return;
        }
        for (auto c0 : chars) {
            for (int c : G[v]) {
                if (c == p) continue;
                for (auto [c12, x] : cnt[c]) {
                    string c012 = string(1, c0) + c12;
                    string c01 = string(1, c0) + c12[0];

                    cnt[v][c01] += x;
                    val[v][c01] += val[c][c12];

                    if (c012 == w || c012 == wr) {
                        val[v][c01] += x;
                    }
                }
            }
        }
    };
    dfs(dfs, 0, -1);
    ll ans = 0;
    for (auto [_, x] : val[0]) chmax(ans, x);
    cout << ans << endl;
}