#include<bits/stdc++.h>
using namespace std;

#define int long long
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define all(v) (v).begin(),(v).end()
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
#define pb push_back
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

int N;
string S;

vint G[100000];

int ans;
int allC,allW;
int C[100000],W[100000];
void dfs(int v,int p){
    if(S[v]=='c')C[v]++;
    else W[v]++;

    for(auto u:G[v]){
        if(u==p)continue;
        dfs(u,v);
        C[v]+=C[u];
        W[v]+=W[u];
    }

    if(S[v]=='c')return;
    for(auto u:G[v]){
        if(u==p)continue;
        ans+=C[u]*(allW-W[u]-1);
    }
    ans+=(allC-C[v])*(W[v]-1);
}

signed main(){
    cin>>N>>S;
    rep(i,N-1){
        int a,b;
        cin>>a>>b;
        a--;b--;
        G[a].pb(b);G[b].pb(a);
    }
    rep(i,N){
        if(S[i]=='c')allC++;
        else allW++;
    }

    dfs(0,-1);
    cout<<ans<<endl;
    return 0;
}