#include <bits/stdc++.h>

using namespace std;

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)

using ll = long long;
using P = std::tuple<int,int>;

const int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1}, dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};

int N;
string nodes;
vector<int> G[100000];

ll rec(int u, int p, int c_cnt, int w_cnt, ll cw_cnt){
    ll res = 0ll;

    if(nodes[u] == 'c'){
        res = 1ll * w_cnt * (w_cnt - 1) / 2;
    }else{
        res = cw_cnt;
    }

    // printf("at %d, get %lld as bonus\n", u, res);

    for(auto v : G[u]){
        if(v == p){continue;}

        if(nodes[u] == 'c'){
            res += rec(v, u, c_cnt + 1, w_cnt, cw_cnt);
        }else{
            res += rec(v, u, c_cnt, w_cnt + 1, cw_cnt + c_cnt);
        }
    }

    return res;
}

tuple<ll,ll,ll> rec2(int u, int p){
    vector<ll> v1, v2;

    ll res = 0ll, all_c_cnt = 0, all_w_cnt = 0;
    
    for(auto v : G[u]){
        if(v == p){continue;}

        ll child_res, c_cnt, w_cnt;
        tie(child_res, c_cnt, w_cnt) = rec2(v, u);

        res += child_res;

        if(nodes[u] == 'w'){
            v1.emplace_back(c_cnt);
            v2.emplace_back(w_cnt);
            all_c_cnt += c_cnt;
            all_w_cnt += w_cnt;
        }
    }
    
    if(nodes[u] == 'w'){
        int l = v1.size();
        for(int i=0;i<l;++i){
            res += (all_c_cnt - v1[i]) * (v2[i] + v2[i] * (v2[i] - 1) / 2);
        }
    }

    if(nodes[u] == 'c'){++all_c_cnt;}
    else{++all_w_cnt;}
    
    return std::make_tuple(res, all_c_cnt, all_w_cnt);
}

int main(){
    //*
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    /*/
      /*/

    std::cin >> N;
    std::cin >> nodes;

    for(int i=0;i<N-1;++i){
        int a, b;
        std::cin >> a >> b;

        --a; --b;
        G[a].emplace_back(b);
        G[b].emplace_back(a);
    }

    ll res = rec(0, -1, 0, 0, 0) + fst(rec2(0, -1));
    printf("%lld\n", res);
}