#include<bits/stdc++.h>

using namespace std;

struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;


typedef long long LL;
template<typename T>
istream& operator>>(istream &is,vector<T> &v){
    for(auto &it:v)is>>it;
    return is;
}
template<typename T>void chmin(T& a, T& b){a=min(a,b);}
template<typename T>void chmax(T& a, T& b){a=max(a,b);}



int N;
string S;
typedef vector<LL> V;
typedef vector<V> Graph;
LL all_c=0,all_w=0;

typedef tuple<LL,LL> P;
P make_tree(int v,int p,Graph& g,Graph &tree,Graph& c_num,Graph& w_num){
    //    cout<<v<<p<<endl;
    LL c=0,w=0;
    for(auto &u:g[v])
        if(u!=p){
            tree[v].push_back(u);
            //cout<<v<<u<<p<<endl;
            LL cc,ww;
            tie(cc,ww)=make_tree(u,v,g,tree,c_num,w_num);
            c_num[v].push_back(cc);
            w_num[v].push_back(ww);
            c+=cc;
            w+=ww;
        }
    if(S[v]=='c')c++;
    else w++;
    return P(c,w);
}
LL dfs(int v,Graph &tree,Graph &c_num,Graph &w_num){
    //cout<<v<<endl;
    LL res=0;
    LL now_w=1,now_c=0;
    for(int i=0;i<(int)tree[v].size();i++){
        //cout<<v<<tree[v][i]<<endl;
        res+=dfs(tree[v][i],tree,c_num,w_num);
        if(S[v]=='w'){
            res+=w_num[v][i]*(all_c-c_num[v][i]);
        }
        now_w+=w_num[v][i];
        now_c+=c_num[v][i];
    }
    if(S[v]=='w'){
        res+=now_c*(all_w-now_w);
    }
    return res;
}

int main(){
    cin>>N>>S;
    Graph g(N),tree(N),c_num(N),w_num(N);
    for(int i=1;i<N;i++){
        int a,b;cin>>a>>b;a--,b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    tie(all_c,all_w)=make_tree(0,0,g,tree,c_num,w_num);
    cout<<dfs(0,tree,c_num,w_num)<<endl;
    return 0;
}