#include<bits/stdc++.h>
using namespace std;
#define V vector
#define pb push_back

typedef long long LL;

void solve() {
    int n; cin >> n;
    V<V<int>> e(n + 1);
    string s; cin >> s;
    for(int i = 1; i < n; i++) {
        int a, b; cin >> a >> b;
        e[a].pb(b);
        e[b].pb(a);
    } 

    auto cal = [&](int x) -> LL {
        if(s[0] == s[2]) return 1LL * x * (x - 1);
        return 1LL * (x / 2) * (x - x / 2);
    };

    if(s.size() == 1) {
        cout << n << endl;
        return;
    } else if(s.size() == 2) {
        if(s[0] == s[1]) cout << 2 * (n - 1) << endl;
        else cout << n - 1 << endl;
        return;
    } else if(s[0] == s[1] && s[1] == s[2]) {
        LL ans = 0;
        for(int i = 1; i <= n; i++) ans += cal(e[i].size());
        cout << ans << endl;
        return;
    }


    V<LL> dp_o_o(n + 1), dp_o_s(n + 1), dp_s(n + 1);

    auto dfs = [&](int x, int p, auto dfs) -> void {
        LL s_sum = 0;
        LL base = 0;
        V<LL> cost(1);
        for(auto y : e[x]) {
            if(y == p) continue;
            dfs(y, x, dfs);
            s_sum += max(dp_o_s[y], dp_s[y]);
            cost.pb(dp_o_o[y] - dp_s[y]);
            base += dp_o_o[y];
        }
        sort(cost.begin() + 1, cost.end());
        // for(auto x : cost) cout << x << " ";
        // cout << endl;
        dp_s[x] = s_sum;
        // cout << " x : " << x << " " << cost.size() << endl;
        for(int i = 0; i < cost.size(); i++) {
            base -= cost[i];
            // cout << base + cal(i) << endl;
            dp_o_s[x] = max(dp_o_s[x], base + cal(i + 1));
            dp_o_o[x] = max(dp_o_o[x], base + cal(i));
        }
    };
    dfs(1, 0, dfs);

    // for(int i = 1; i <= n; i++) cout << dp_s[i] << " ";
    // cout << endl;
    // for(int i = 1; i <= n; i++) cout << dp_o_o[i] << " ";
    // cout << endl;
    // for(int i = 1; i <= n; i++) cout << dp_o_s[i] << " ";
    // cout << endl;

    cout << max(dp_o_o[1], dp_s[1]) << endl;

}

int main() {
    ios::sync_with_stdio(0), cin.tie(0);
    // int t; cin >> t;
    int t = 1;
    while(t--) solve();
}