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

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()
#define bit(n) (1LL<<(n))
#define sz(x) ((int)(x).size())
#define fst first
#define snd second
using ll=long long;using pii=pair<int,int>;using vb=vector<bool>;
using vi=vector<int>;using vvi=vector<vi>;using vvvi=vector<vvi>;
using vl=vector<ll>;using vvl=vector<vl>;using vvvl=vector<vvl>;
using vd=vector<double>;using vvd=vector<vd>;using vvvd=vector<vvd>;
using vpii=vector<pii>;using vvpii=vector<vpii>;using vvvpii=vector<vvpii>;
template <typename T> T read() {T t; cin >> t; return t;}

void Main() {
  int n = read<int>();
  auto s = read<string>();
  vvi E(n);
  rep(i, n-1) {
    int u = read<int>() - 1;
    int v = read<int>() - 1;
    E[u].push_back(v);
    E[v].push_back(u);
  }

  vi ww(n), w(n);

  function<void(int, int)> dfs1 = [&](int cur, int pre) {
    forr(nex, E[cur]) if (nex != pre) {
      dfs1(nex, cur);
      w[cur] += w[nex];
      ww[cur] += ww[nex];
    }
    if (s[cur] == 'w') {
      ww[cur] += w[cur];
      w[cur]++;
    }
  };

  ll ans = 0;

  function<void(int, int, int, int)> dfs2 = [&](int cur, int pre, int nww, int nw) {
    //_p("dfs2(%d,%d,%d,%d)\n",cur,pre,nww,nw);
    if (s[cur] == 'c') {
      ans += ww[cur];
      ans += nww;
    }

    forr(nex, E[cur]) if (nex != pre) {
      int nex_nw, nex_nww;
      if (s[cur] == 'w') {
        nex_nww = nww + nw + (w[cur] - w[nex] - 1);
        nex_nw = nw + (w[cur] - w[nex]);
      }
      else {
        nex_nww = nww + (ww[cur] - ww[nex]);
        nex_nw = nw + (w[cur] - w[nex]);

      }
      dfs2(nex, cur, nex_nww, nex_nw);
    }
  };

  rep(i, n) if (s[i] == 'c') {
    dfs1(i, -1);
    //cout<<"i: "<<i<<endl;
    //cout << "w:"; rep(ii,sz(w)) cout << ' ' << w[ii]; cout << endl;
    //cout << "ww:"; rep(ii,sz(ww)) cout << ' ' << ww[ii]; cout << endl;
    dfs2(i, -1, 0, 0);
    break;
  }

  cout << ans << endl;
}
int main() { cin.tie(nullptr); ios::sync_with_stdio(false); Main(); return 0; }