#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

// using mint = modint998244353;

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

using mint = modint;

void dfs(vector<vector<ll>> &graph, vector<bool> &isvisited, ll v,
         vector<vector<ll>> &treedp, string &S) {
    isvisited[v] = true;
    ll ret1 = 0;
    ll ret2 = 0;
    if (S[v] == 'c') {
        ret1 += 1;
    } else {
        ret2 += 1;
    }
    for (ll x : graph[v]) {
        if (isvisited[x]) {
            continue;
        }
        dfs(graph, isvisited, x, treedp, S);
        ret1 += treedp[x][0];
        ret2 += treedp[x][1];
    }
    treedp[v][0] = ret1;
    treedp[v][1] = ret2;
}

int main() {
    ll N;
    cin >> N;
    string S;
    cin >> S;
    vector<ll> a(N - 1);
    vector<ll> b(N - 1);
    for (ll i = 0; i < N - 1; i++) {
        cin >> a[i] >> b[i];
        a[i]--;
        b[i]--;
    }
    vector<vector<ll>> graph(N, vector<ll>(0));
    for (ll i = 0; i < N - 1; i++) {
        graph[a[i]].push_back(b[i]);
        graph[b[i]].push_back(a[i]);
    }
    vector<vector<ll>> treedp(N, vector<ll>(2, 0));
    vector<bool> isvisited(N, false);
    dfs(graph, isvisited, 0, treedp, S);
    // debug(treedp);
    ll ans = 0;
    ll all_c = treedp[0][0];
    ll all_w = treedp[0][1];
    for (ll i = 0; i < N; i++) {
        if (S[i] == 'c') {
            continue;
        }
        ll upc = all_c;
        ll upw = all_w - 1;
        for (ll j = 0; j < graph[i].size(); j++) {
            ll cnt_c = treedp[graph[i][j]][0];
            ll cnt_w = treedp[graph[i][j]][1];
            if (cnt_c + cnt_w <= treedp[i][0] + treedp[i][1]) {
                upc -= cnt_c;
                upw -= cnt_w;
            }
        }
        for (ll j = 0; j < graph[i].size(); j++) {
            ll cnt_c = treedp[graph[i][j]][0];
            ll cnt_w = treedp[graph[i][j]][1];
            if (cnt_c + cnt_w <= treedp[i][0] + treedp[i][1]) {
                ans += cnt_c * upw;
                ans += cnt_w * (all_c - cnt_c);
            }
        }
    }
    cout << ans << endl;
}