#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define vtpl(x,y,z) vector<tuple<x,y,z>>
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e17;
const ll dy[9]={0,1,-1,0,1,1,-1,-1,0};
const ll dx[9]={1,0,0,-1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
ll C=0,W=0;
ll ans=0;
vvl g(100010);
vl wis(100010);
pl dfs(ll v,ll par=-1){
  vl c,w;
  for(auto p:g[v]){
    if(p==par)continue;
    auto [a,b]=dfs(p,v);
    c.emplace_back(a);
    w.emplace_back(b);
  }
  ll sumc=accumulate(all(c),0LL);
  ll sumw=accumulate(all(w),0LL);
  c.emplace_back(C-sumc-(wis[v]^1));
  w.emplace_back(W-sumw-wis[v]);
  ll ret=0;
  if(wis[v]){
    rep(i,c.size()){
      ret+=c[i]*(W-wis[v]-w[i]);
    }
    sumw++;
  }
  else sumc++;
  ans+=ret;
  //cout << v  << endl;
  //for(auto p:c)cout << p <<" ";cout << endl;
  //for(auto p:w)cout << p <<" ";cout << endl;
  return make_pair(sumc,sumw);
}
int main(){
  ll n;cin >> n;
  rep(i,n){
    char x;cin >> x;
    if(x=='w'){
      wis[i]++;
      W++;
    }
    else C++;
  }
  rep(i,n-1){
    ll a,b;cin >> a >> b;a--;b--;
    g[a].emplace_back(b);
    g[b].emplace_back(a);
  }
  dfs(0);
  cout << ans << endl;
}