#include "bits/stdc++.h"
#ifdef DEBUG
#include "algo/debug.hpp"
#else
#define dbg(...)
#define dbgm(...)
#endif
using namespace std;
typedef long long ll;
typedef unsigned int ui;
typedef unsigned long long ull;
typedef pair<int, int> pi;
typedef pair<ll, ll> pll;
// using u128 = __uint128_t;
// using i128 = __int128;
const int mod = 1000000007;
const int N = 300005;
const int LOG = 20;
const int inf = 1e9;
const double eps = 1e-11;
int n, m, k, qq;
string s;
vector<int> adj[N];
int type;
ll dp[N][2][2];
int deg[N];
void dfs(int u, int p = -1) {
    for (int v : adj[u]) {
        if (v == p) continue;
        dfs(v, u);
    }
    
    for (int x = 0; x < 2; x++) {
        vector<ll> a;
        ll cur = 0;
        for (int v : adj[u]) {
            if (v == p) continue;
            a.push_back(dp[v][1][x] - dp[v][0][x]);
            cur += dp[v][0][x];
        }
        
        sort(a.rbegin(), a.rend());
        int sz = a.size();
        for (int y = 0; y < (u ? 2 : 1); y++) {
            for (int i = 0;; i++) {
                ll z = y + i, d = deg[u], val;
                if (type == 0) val = (d - z) * (d - z - 1);
                if (type == 1) val = z * (d - z);
                if (type == 2) val = z * (z - 1);
                if (type == 3) val = (z / 2) * ((z + 1) / 2);
                if (x) val = 0;
                dp[u][x][y] = max(dp[u][x][y], cur + val);
                if (i == sz) break;
                cur += a[i];
            }
        }
    }
}

void solve() {
    cin >> n >> s;
    for (int i = 0; i < n - 1; i++) {
        int u, v;
        cin >> u >> v;
        u--, v--;
        deg[u]++, deg[v]++;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    
    if (s.size() == 1) {
        cout << n << "\n";
    }
    
    else if (s.size() == 2) {
        int x = (n - 1) * (s[0] == s[1] ? 2 : 1);
        cout << x << "\n";
    }
    
    else {
        if (s[0] == s[1] && s[1] == s[2]) type = 0;
        else if ((s[0] == s[1] && s[1] != s[2]) || (s[0] != s[1] && s[1] == s[2])) type = 1;
        else if (s[0] == s[2] && s[0] != s[1]) type = 2;
        else type = 3;
        dfs(0);
        cout << max(dp[0][0][0], dp[0][1][0]) << "\n";
    }
}

int32_t main() {
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    solve();
}