using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Diagnostics;
using Enu = System.Linq.Enumerable;
using System.Numerics;

public class Program
{
    long ans = 0;
    int[] Val;
    List<int>[] G;

    public void Solve()
    {
        int N = Reader.Int();
        Val = Reader.String().Select(c => c == 'c' ? 0 : 1).ToArray();
        G = Enu.Range(0, N).Select(i => new List<int>()).ToArray();
        for (int i = 0; i < N - 1; i++)
        {
            int a = Reader.Int() - 1, b = Reader.Int() - 1;
            G[a].Add(b);
            G[b].Add(a);
        }
        var who = new List<int>();
        var pos = new List<int>[N];
        for (int i = 0; i < N; i++) pos[i] = new List<int>();
        Rec(0, -1, G, Val, who, pos);
        long totalA = Val.Count(c => c == 0);
        long totalB = N - totalA;
        var As = new long[who.Count];
        var Bs = new long[who.Count];

        for (int i = 0; i < who.Count; i++)
            if (i == pos[who[i]][0])
                if (Val[who[i]] == 0) As[i]++;
                else Bs[i]++;
        for (int i = 1; i < As.Length; i++) { As[i] += As[i - 1]; Bs[i] += Bs[i - 1]; }

        for (int root = 0; root < N; root++)
            if (Val[root] == 1)
            {
                long remA = totalA, remB = totalB - 1, curr = 0;
                for (int i = 0; i + 1 < pos[root].Count; i++)
                {
                    int L = pos[root][i], R = pos[root][i + 1] - 1;
                    long a = As[R] - As[L];
                    long b = Bs[R] - Bs[L];
                    curr += a * (totalB - 1 - b);
                    curr += b * (totalA - a);
                    remA -= a;
                    remB -= b;
                }
                curr += remA * (totalB - 1 - remB);
                curr += remB * (totalA - remA);
                ans += curr / 2;
            }
        Console.WriteLine(ans);
        Console.ReadLine();
    }

    void Rec(int a, int prev, List<int>[] G, int[] Val, List<int> who, List<int>[] positions)
    {
        positions[a].Add(who.Count);
        who.Add(a);
        foreach (int b in G[a])
            if (b != prev)
            {
                Rec(b, a, G, Val, who, positions);
                positions[a].Add(who.Count);
                who.Add(a);
            }
    }

}


class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    static TextReader reader = Console.In;
    static readonly char[] separator = { ' ' };
    static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    static string[] A = new string[0];
    static int i;
    static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Range(N, Int); }
    public static int[][] IntTable(int H) { return Range(H, IntLine); }
    public static string[] StringArray(int N) { return Range(N, Next); }
    public static string[][] StringTable(int N) { return Range(N, () => Split(Line())); }
    public static string Line() { return reader.ReadLine().Trim(); }
    static string[] Split(string s) { return s.Split(separator, op); }
    static T[] Range<T>(int N, Func<T> f) { var r = new T[N]; for (int i = 0; i < N; r[i++] = f()) ; return r; }
    static string Next() { CheckNext(); return A[i++]; }
    static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}