#include<bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N;
  string S;
  cin >> S;
  int all_w = 0;
  for (int i = 0; i < N; i++) {
    if (S[i] == 'w') {
      all_w++;
    }
  }
  vector<vector<int>> E(N);
  for (int i = 0; i < N - 1; i++) {
    int u, v;
    cin >> u >> v;
    u--;
    v--;
    E[u].push_back(v);
    E[v].push_back(u);
  }
  queue<int> Q;
  int zero = 0;
  for (int i = 0; i < N; i++) {
    if (S[i] == 'c') {
      zero = i;
      break;
    }
  }
  Q.push(zero);
  vector<int> p(N, -1);
  vector<vector<int>> c(N);
  vector<int> bfs;
  while (!Q.empty()) {
    int v = Q.front();
    Q.pop();
    bfs.push_back(v);
    for (int w : E[v]) {
      if (w != p[v]) {
        p[w] = v;
        c[v].push_back(w);
        Q.push(w);
      }
    }
  }
  reverse(bfs.begin(), bfs.end());
  vector<long long> dp1(N);//w
  vector<long long> dp2(N);//ww
  for (int v : bfs) {
    for (int w : c[v]) {
      dp1[v] += dp1[w];
      if (S[v] == 'w') {
        dp2[v] += dp1[w];
      }
      dp2[v] += dp2[w];
    }
    if (S[v] == 'w') {
      dp1[v]++;
    }
  }
  reverse(bfs.begin(), bfs.end());
  vector<long long> dp3(N);//辺を張り替えてからのww
  for (int v : bfs) {
    //S[v] == 'w'かどうかで変わる。
    long long sum = 0;
    long long cntw = 0;
    for (int w : c[v]) {
      sum += dp2[w];
      cntw += dp1[w];
    }
    for (int w : c[v]) {
      long long sum1 = cntw - dp1[w];
      long long sum2 = sum - dp2[w];
      if (S[v] == 'w') {
        sum2 += sum1;
        sum2 += all_w - dp1[v];
      }
      sum2 += dp3[v];
      dp3[w] = sum2;
    }
  }
  long long ans = 0;
  for (int i = 0; i < N; i++) {
    if (S[i] == 'c') {
      ans += dp2[i] + dp3[i];
    }
  }
  cout << ans << endl;
}