/**
 * @file qoj8213-1.cpp
 * @author n685
 * @brief
 * @date 2024-02-18
 *
 *
 */
#include <bits/stdc++.h>

#ifdef LOCAL
#include "dd/debug.h"
#else
#define dbg(...) 42
#define dbgR(...) 4242
#define dbgP(...) 420
#define dbgRP(...) 420420
void nline() {}
#endif

int main() {
#ifndef LOCAL
  std::cin.tie(nullptr)->sync_with_stdio(false);
#endif

  int n;
  std::cin >> n;
  std::string w;
  std::cin >> w;
  if ((int)w.size() == 1) {
    std::cout << n << '\n';
    return 0;
  } else if ((int)w.size() == 2) {
    std::cout << ((w[0] == w[1]) + 1) * (n - 1) << '\n';
    return 0;
  }
  if (w[0] == w[1]) {
    std::swap(w[0], w[2]);
  }
  int type;
  if (w[0] == w[1] && w[1] == w[2]) {
    type = 0;
  } else if (w[0] != w[1] && w[0] == w[2]) {
    type = 1;
  } else if (w[0] != w[1] && w[1] == w[2]) {
    type = 2;
  } else {
    type = 3;
  }

  std::vector<std::vector<int>> adj(n);
  for (int i = 0; i < n - 1; ++i) {
    int u, v;
    std::cin >> u >> v;
    --u;
    --v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  if (type == 0) {
    int64_t ans = 0;
    for (int i = 0; i < n; ++i) {
      int64_t k = (int)adj[i].size();
      ans += k * (k - 1);
    }
    std::cout << ans << '\n';
    return 0;
  }
  --type;

  std::vector<std::array<std::array<int64_t, 2>, 2>> dp(n);
  const std::array<std::function<int64_t(int64_t, int)>, 3> tr{
      [](int64_t v, [[maybe_unused]] int deg) { return v * (v - 1); },
      [](int64_t v, int deg) { return v * (deg - v); },
      [](int64_t v, [[maybe_unused]] int deg) {
        return (v / 2) * ((v + 1) / 2);
      }};
  auto dfs = [&](auto &self, int node, int par) -> void {
    int deg = (int)adj[node].size();
    std::vector<int64_t> ch;
    for (int i : adj[node]) {
      if (i == par) {
        continue;
      }
      self(self, i, node);
      dp[node][0][0] += dp[i][0][0];
      dp[node][0][1] += dp[i][0][0];
      dp[node][1][0] += std::max(dp[i][0][1], dp[i][1][1]);
      dp[node][1][1] += std::max(dp[i][0][1], dp[i][1][1]);
      ch.push_back(dp[i][1][0] - dp[i][0][0]);
    }
    int64_t sum = dp[node][0][0];
    dp[node][0][1] += tr[type](1, deg);
    std::sort(ch.begin(), ch.end(), std::greater<>());
    for (int i = 0; i < (int)ch.size(); ++i) {
      sum += ch[i];
      dp[node][0][0] = std::max(dp[node][0][0], sum + tr[type](i + 1, deg));
      dp[node][0][1] = std::max(dp[node][0][1], sum + tr[type](i + 2, deg));
    }
  };
  dfs(dfs, 0, -1);
  std::cout << std::max(dp[0][0][0], dp[0][1][0]) << '\n';
}