using System; using System.Collections.Generic; using System.Linq; using System.Linq.Expressions; using System.IO; using Binary = System.Func; using Unary = System.Func; class Program { static StreamWriter sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; const int M = 1000000007; const double eps = 1e-9; static int[] dd = { 0, 1, 0, -1, 0 }; static int n; static string s; static List[] edge; static int[] chw; static int[] chc; static int[] pare; static void Main() { var sc = new Scan(); n = sc.Int; s = sc.Str; edge = new List[n]; chw = new int[n]; chc = new int[n]; pare = new int[n]; for (int i = 0; i < n; i++) { edge[i] = new List(); } for (int i = 0; i < n - 1; i++) { var a = sc.IntArr; edge[a[0] - 1].Add(a[1] - 1); edge[a[1] - 1].Add(a[0] - 1); } dfs(0, -1); long ans = 0; for (int i = 0; i < n; i++) { if (s[i] == 'c') continue; int wc = chw[0]; int cc = chc[0]; ans += wc * cc; foreach (var item in edge[i]) { if (item == pare[i]) continue; ans -= chw[item] * chc[item]; wc -= chw[item]; cc -= chc[item]; } ans -= wc * cc; } sw.WriteLine(ans); sw.Flush(); } static void dfs(int i, int par) { pare[i] = par; if (edge[i].Count == 1) { chw[i] = s[i] == 'w' ? 1 : 0; chc[i] = s[i] == 'c' ? 1 : 0; return; } foreach (var item in edge[i]) { if (item == par) continue; dfs(item, i); chw[i] += chw[item]; chc[i] += chc[item]; } return; } static void swap(ref T a, ref T b) { var t = a; a = b; b = t; } static T Max(params T[] a) => a.Max(); static T Min(params T[] a) => a.Min(); static void DBG(params T[] a) => Console.WriteLine(string.Join(" ", a)); static void DBG(params object[] a) => Console.WriteLine(string.Join(" ", a)); static void Prt(params T[] a) => sw.WriteLine(string.Join(" ", a)); static void Prt(params object[] a) => sw.WriteLine(string.Join(" ", a)); } static class ex { public static void swap(this IList a, int i, int j) { var t = a[i]; a[i] = a[j]; a[j] = t; } public static T[] copy(this IList a) { var ret = new T[a.Count]; for (int i = 0; i < a.Count; i++) ret[i] = a[i]; return ret; } } public static class Operator { static readonly ParameterExpression x = Expression.Parameter(typeof(T), "x"); static readonly ParameterExpression y = Expression.Parameter(typeof(T), "y"); public static readonly Func Add = Lambda(Expression.Add); public static readonly Func Subtract = Lambda(Expression.Subtract); public static readonly Func Multiply = Lambda(Expression.Multiply); public static readonly Func Divide = Lambda(Expression.Divide); public static readonly Func Plus = Lambda(Expression.UnaryPlus); public static readonly Func Negate = Lambda(Expression.Negate); public static Func Lambda(Binary op) => Expression.Lambda>(op(x, y), x, y).Compile(); public static Func Lambda(Unary op) => Expression.Lambda>(op(x), x).Compile(); } class ScanCHK : Scan { public new string Str { get { var s = Console.ReadLine(); return s == s.Trim() ? s : ""; } } } class Scan { public int Int => int.Parse(Str); public long Long => long.Parse(Str); public double Double => double.Parse(Str); public string Str => Console.ReadLine().Trim(); public int[] IntArr => StrArr.Select(int.Parse).ToArray(); public long[] LongArr => StrArr.Select(long.Parse).ToArray(); public double[] DoubleArr => StrArr.Select(double.Parse).ToArray(); public string[] StrArr => Str.Split(); bool eq() => typeof(T).Equals(typeof(U)); T ct(U inp) => (T)Convert.ChangeType(inp, typeof(T)); T cv(string inp) => eq() ? ct(int.Parse(inp)) : eq() ? ct(long.Parse(inp)) : eq() ? ct(double.Parse(inp)) : eq() ? ct(inp[0]) : ct(inp); public void Multi(out T a) => a = cv(Str); public void Multi(out T a, out U b) { var ar = StrArr; a = cv(ar[0]); b = cv(ar[1]); } public void Multi(out T a, out U b, out V c) { var ar = StrArr; a = cv(ar[0]); b = cv(ar[1]); c = cv(ar[2]); } public void Multi(out T a, out U b, out V c, out W d) { var ar = StrArr; a = cv(ar[0]); b = cv(ar[1]); c = cv(ar[2]); d = cv(ar[3]); } public void Multi(out T a, out U b, out V c, out W d, out X e) { var ar = StrArr; a = cv(ar[0]); b = cv(ar[1]); c = cv(ar[2]); d = cv(ar[3]); e = cv(ar[4]); } } class mymath { long Mod = 1000000007; public void setMod(long m) => Mod = m; public bool isprime(long a) { if (a < 2) return false; for (long i = 2; i * i <= a; i++) if (a % i == 0) return false; return true; } public bool[] sieve(int n) { var p = new bool[n + 1]; for (int i = 2; i <= n; i++) p[i] = true; for (int i = 2; i * i <= n; i++) if (p[i]) for (int j = i * i; j <= n; j += i) p[j] = false; return p; } public List getprimes(int n) { var prs = new List(); var p = sieve(n); for (int i = 2; i <= n; i++) if (p[i]) prs.Add(i); return prs; } public long[][] E(int n) { var ret = new long[n][]; for (int i = 0; i < n; i++) { ret[i] = new long[n]; ret[i][i] = 1; } return ret; } public long[][] pow(long[][] A, long n) { if (n == 0) return E(A.Length); var t = pow(A, n / 2); if ((n & 1) == 0) return mul(t, t); return mul(mul(t, t), A); } public long dot(long[] x, long[] y) { int n = x.Length; long ret = 0; for (int i = 0; i < n; i++) ret = (ret + x[i] * y[i]) % Mod; return ret; } public long[][] trans(long[][] A) { int n = A[0].Length, m = A.Length; var ret = new long[n][]; for (int i = 0; i < n; i++) { ret[i] = new long[m]; for (int j = 0; j < m; j++) ret[i][j] = A[j][i]; } return ret; } public long[] mul(long[][] A, long[] x) { int n = A.Length; var ret = new long[n]; for (int i = 0; i < n; i++) ret[i] = dot(x, A[i]); return ret; } public long[][] mul(long[][] A, long[][] B) { int n = A.Length; var Bt = trans(B); var ret = new long[n][]; for (int i = 0; i < n; i++) ret[i] = mul(Bt, A[i]); return ret; } public long[] add(long[] x, long[] y) { int n = x.Length; var ret = new long[n]; for (int i = 0; i < n; i++) ret[i] = (x[i] + y[i]) % Mod; return ret; } public long[][] add(long[][] A, long[][] B) { int n = A.Length; var ret = new long[n][]; for (int i = 0; i < n; i++) ret[i] = add(A[i], B[i]); return ret; } public long pow(long a, long b) { if (a >= Mod) return pow(a % Mod, b); if (a == 0) return 0; if (b == 0) return 1; var t = pow(a, b / 2); if ((b & 1) == 0) return t * t % Mod; return t * t % Mod * a % Mod; } public long inv(long a) => pow(a, Mod - 2); public long gcd(long a, long b) { while (b > 0) { var t = a % b; a = b; b = t; } return a; } public long extgcd(long a, long b, out long x, out long y) { long g = a; x = 1; y = 0; if (b != 0) { g = extgcd(b, a % b, out y, out x); y -= (a / b) * x; } return g; } public long lcm(long a, long b) => a * (b / gcd(a, b)); public long comb(int n, int r) { if (n < 0 || r < 0 || r > n) return 0; if (n - r < r) r = n - r; if (r == 0) return 1; if (r == 1) return n; int[] numer = new int[r], denom = new int[r]; for (int k = 0; k < r; k++) { numer[k] = n - r + k + 1; denom[k] = k + 1; } for (int p = 2; p <= r; p++) { int piv = denom[p - 1]; if (piv > 1) { int ofst = (n - r) % p; for (int k = p - 1; k < r; k += p) { numer[k - ofst] /= piv; denom[k] /= piv; } } } long ret = 1; for (int k = 0; k < r; k++) if (numer[k] > 1) ret = ret * numer[k] % Mod; return ret; } }