//四則演算 #pragma GCC target("avx")
//並列計算 #pragma GCC optimize("O3")
//条件分岐を減らす #pragma GCC optimize("unroll-loops")
//浮動小数点演算 #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define eFOR(i,a,n) for(int i=(a);i<=(n);++i)
#define rFOR(i,a,n) for(int i=(n)-1;i>=(a);--i)
#define erFOR(i,a,n) for(int i=(n);i>=(a);--i)
#define each(i, a) for(auto &i : a)
#define SORT(a) sort(a.begin(),a.end())
#define rSORT(a) sort(a.rbegin(),a.rend())
#define fSORT(a,f) sort(a.begin(),a.end(),f)
#define all(a) a.begin(),a.end()
#define out(y,x) ((y)<0||h<=(y)||(x)<0||w<=(x))
#define tp(a,i) get<i>(a)
#define line cout << "-----------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause")
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T>inline istream& operator>>(istream& is, deque<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }
template<class T>inline void print(const T& a) { cout << a << "\n"; }
template<class T1, class T2>inline void print(const pair<T1, T2>& a) { cout << a.first << " " << a.second << "\n"; }
template<class T, class... Ts>inline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); }
template<class T>inline void print(const vector<T>& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << "\n"; }
template<class T1, class T2>inline void print(const vector<pair<T1, T2>>& v) { for (auto& a : v)print(a); }
template<class T>inline void print(const vector<vector<T>>& v) { for (auto& a : v)print(a); }
inline string reversed(const string& s) { string t = s; reverse(all(t)); return t; }

pair<ll, ll> operator+=(pair<ll, ll>& x, const pair<ll, ll>& y) {
    x.first += y.first;
    x.second += y.second;
    return x;
}
pair<ll, ll> operator+(pair<ll, ll> x, const pair<ll, ll> y) {
    return x += y;
}
pair<ll, ll> operator-=(pair<ll, ll>& x, const pair<ll, ll>& y) {
    x.first -= y.first;
    x.second -= y.second;
    return x;
}
pair<ll, ll> operator-(pair<ll, ll> x, const pair<ll, ll> y) {
    return x -= y;
}

int main() {
    init();

    int n; cin >> n;
    string s; cin >> s;
    vector<VI> g(n);
    FOR(i, 0, n - 1) {
        int a, b; cin >> a >> b;
        --a, --b;
        g[a].push_back(b);
        g[b].push_back(a);
    }


#define w first
#define c second

    vector<pair<ll, ll>> wc(n);
    {
        auto dfs = [&](auto&& f, int cur, int par)->void {
            if (s[cur] == 'w')++wc[cur].w;
            else ++wc[cur].c;
            int idx = -1, sz = g[cur].size();
            for (int i = 0, to; i < sz; ++i) {
                to = g[cur][i];
                if (to == par)idx = i;
                else {
                    f(f, to, cur);
                    wc[cur].w += wc[to].w;
                    wc[cur].c += wc[to].c;
                }
            }
            if (idx != -1)g[cur].erase(g[cur].begin() + idx);
        };
        dfs(dfs, 0, -1);
    }

    ll ans = 0;
    {
        auto dfs = [&](auto&& f, int cur, pair<ll, ll> x)->void {
            int sz = g[cur].size();
            vector<pair<ll, ll>> l(sz), r(sz);
            pair<ll, ll> y = s[cur] == 'w' ? pair<ll, ll>(1LL, 0LL) : pair<ll, ll>(0LL, 1LL);
            for (int i = 0, to; i < sz; ++i) {
                to = g[cur][i];
                if (i < sz - 1)l[i + 1] = wc[to] + l[i];
                if (0 < i)r[i - 1] = wc[to];
            }
            rFOR(i, 0, sz - 1)r[i] += r[i + 1];

            if (s[cur] == 'w') {
                ans += x.w * (wc[cur] - y).c;
                ans += x.c * (wc[cur] - y).w;
            }
            for (int i = 0, to; i < sz; ++i) {
                to = g[cur][i];
                f(f, to, x + l[i] + r[i] + y);
            }
        };
        dfs(dfs, 0, pair<ll, ll>());
    }

    print(ans);

    return 0;
}