#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back
#define pcnt __builtin_popcount
#define show(x) cout<<#x<<" = "<<x<<endl;
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define fi first
#define se second
#define rng(a) a.begin(),a.end()
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define sz(x) (int)(x).size()
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef set<int> si;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pll> vpll;
typedef set<ll> sl;
template<typename T>string join(vector<T>&v)
{stringstream s;FOR(i,0,sz(v))s<<' '<<v[i];return s.str().substr(1);}
ll gcd(ll a,ll b){if(a>b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;}
int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;}
void dout(double d){printf("%.12f\n",d);}

const int iinf = 1e9;
const ll linf = 1e18;
const int mod = 1e9+7;
const double pi = acos(-1);
const double eps = 1e-10;
int n;
string s;
ll ans;
vi E[100005];

typedef pair<pll, pll> ql;
ql search(int a, int p){
  ll c = 0, w = 0, cw = 0, ww = 0;
  ll sc = 0, sw = 0, scw = 0, sww = 0;
  each(itr, E[a]){
    if(*itr == p)continue;
    ql r = search(*itr, a);
    ans += r.fi.fi * sww;
    ans += r.fi.se * scw;
    ans += r.se.fi * sw;
    ans += r.se.se * sc;
    if(s[a] == 'c'){
      ans += r.se.se;
    }else{
      ans += r.se.fi;
      ans += sc * r.fi.se;
      ans += sw * r.fi.fi;
    }
    sc += r.fi.fi;
    sw += r.fi.se;
    scw += r.se.fi;
    sww += r.se.se;
  }
  if(s[a] == 'c'){
    c = sc + 1;
    w = sw;
    cw = scw;
    ww = sww;
  }else{
    c = sc;
    w = sw + 1;
    cw = scw + sc;
    ww = sww + sw;
  }
  return mp(mp(c,w),mp(cw,ww));
}

main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> s;
  FOR(i, 1, n){
    int a, b;
    cin >> a >> b;
    a--;b--;
    E[a].pb(b);
    E[b].pb(a);
  }
  search(0, -1);
  cout << ans << endl;
  return 0;
}