#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<numeric>
#include<cmath>
#include<utility>
#include<tuple>
#include<cstdint>
#include<cstdio>
#include<iomanip>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<deque>
#include<unordered_map>
#include<unordered_set>
#include<bitset>
#include<cctype>
#include<chrono>
#include<random>
#include<cassert>
#include<cstddef>
#include<iterator>
#include<string_view>
#include<type_traits>

#ifdef LOCAL
#  include "debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

using namespace std;
#define rep(i,n) for(int i=0; i<(n); i++)
#define rrep(i,n) for(int i=(n)-1; i>=0; i--)
#define FOR(i,a,b) for(int i=(a); i<(b); i++)
#define RFOR(i,a,b) for(int i=(b-1); i>=(a); i--)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define pb push_back
using ll = long long;
using D = double;
using LD = long double;
using P = pair<int, int>;
template<typename T> using PQ = priority_queue<T,vector<T>>;
template<typename T> using minPQ = priority_queue<T, vector<T>, greater<T>>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
void yesno(bool flag) {cout << (flag?"Yes":"No") << "\n";}

template<typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
template<typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template<typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (auto &x : v) is >> x;
    return is;
}
void in() {}
template<typename T, class... U>
void in(T &t, U &...u) {
    cin >> t;
    in(u...);
}
void out() { cout << "\n"; }
template<typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u) {
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}
void outr() {}
template<typename T, class... U, char sep = ' '>
void outr(const T &t, const U &...u) {
    cout << t;
    outr(u...);
}

const int MAX_N = 100005;

string s;
vector<int> g[MAX_N];

struct var {
    ll cnt, sz;
    var(ll cnt = 0, ll sz = 0): cnt(cnt), sz(sz) {}
    var operator+ (const var& a) const {
        return {cnt+a.cnt, sz+a.sz};
    }
    var addRoot(int v) const {
        if(s[v] == 'w'){
            return {cnt+sz, sz+1};
        }
        else{
            return *this;
        }
    }
};

vector<var> dp[MAX_N];
var ans[MAX_N];

var dfs1(int v, int p = -1) {
    var dpsum;
    dp[v] = vector<var> (g[v].size());

    rep(i, g[v].size()) {
        int u = g[v][i];
        if(u == p) continue;
        dp[v][i] = dfs1(u, v);
        dpsum = dpsum + dp[v][i];
    }
    return dpsum.addRoot(v);
}

void dfs2(int v, const var& dpParent = var(), int p = -1) {
    int deg = g[v].size();
    rep(i, deg) if(g[v][i] == p) dp[v][i] = dpParent;

    vector<var> dpSum_Left(deg+1), dpSum_Right(deg+1);
    rep(i,deg) dpSum_Left[i+1] = dpSum_Left[i] + dp[v][i];
    rrep(i, deg) dpSum_Right[i] = dpSum_Right[i+1] + dp[v][i];

    ans[v] = dpSum_Left[deg].addRoot(v);

    rep(i,deg) {
        int u = g[v][i];
        if(u == p) continue;
        var d = dpSum_Left[i] + dpSum_Right[i+1];
        dfs2(u, d.addRoot(v), v);
    }
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; cin >> n >> s;
    rep(i,n-1) {
        int a,b; cin >> a >> b; a--; b--;
        g[a].pb(b); g[b].pb(a);
    }
    dfs1(0);
    dfs2(0);
    ll res = 0;
    rep(i,n){
        if(s[i] == 'c') res += ans[i].cnt;
    }
    out(res);
}