using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Text;
using System.Linq;

using E = System.Linq.Enumerable;
using System.Threading;

internal partial class Solver {
    public void Run() {
        var n = ni();
        var adj = Enumerable.Range(0, n).Select(_ => new List<int>()).ToArray();
        for (int i = 0; i < n - 1; i++) {
            var x = ni() - 1;
            var y = ni() - 1;
            adj[x].Add(y);
            adj[y].Add(x);
        }
        var s = ns();

        var wnum = s.Count(c => c == 'W');
        if (wnum == 0) {
            cout.WriteLine(0);
        } else if (wnum == 1) {
            cout.WriteLine(1);
        } else {
            var queue = new Queue<int>();
            for (int i = 0; i < n; i++) {
                if (adj[i].Count == 1) queue.Enqueue(i);
            }
            while (queue.Count > 0) {
                var now = queue.Dequeue();
                if (s[now] == 'B' && adj[now].Count == 1) {
                    var next = adj[now][0];
                    if (s[next] == 'B') {
                        queue.Enqueue(next);
                    }
                    adj[now].Clear();
                    if (!adj[next].Remove(now)) throw new Exception();
                }
            }
            var isBlack = new bool[n];
            for (int i = 0; i < n; i++) {
                var degree = adj[i].Count;
                if (degree == 1 && s[i] == 'B') throw new Exception();
                if (degree % 2 == 1) isBlack[i] = (s[i] == 'W');
                else isBlack[i] = (s[i] == 'B');
            }
            int degreeSum = 0, root = -1;
            var reRooting = new ReRooting<int>((a, b) => {
                return Math.Max(a, b);
            }, (v, index) => {
                return (!isBlack[index] ? 1 : 0) + v;
            }, 0);
            for (int i = 0; i < n; i++) {
                if (adj[i].Count > 0) {
                    degreeSum += adj[i].Count;
                    root = i;
                    if (!isBlack[i]) degreeSum++;
                }
            }
#if true
            var res = reRooting.Solve(adj, root);
            var ans = degreeSum - 2 * E.Range(0, n).Select(i => res[i]).Max();
#else
            int max = 0;
            int dfs(int pos, int parent) {
                var d = new List<int> { 0, 0 };
                foreach (var child in adj[pos]) {
                    if (child == parent) continue;
                    d.Add(dfs(child, pos));
                }
                d.Sort();
                d.Reverse();
                int v = isBlack[pos] ? 0 : 1;
                max = Math.Max(max, v + d[0] + d[1]);
                return v + d[0];
            }
            dfs(root, -1);
            var ans = degreeSum - 2 * max;
#endif

            cout.WriteLine(ans);
        }
    }

}

// PREWRITEN CODE BEGINS FROM HERE

static public class StringExtensions {
    static public string JoinToString<T>(this IEnumerable<T> source, string separator = " ") {
        return string.Join(separator, source);
    }
}

public class ReRooting<TMonoid> {
    private readonly TMonoid _identity;
    private readonly Func<TMonoid, TMonoid, TMonoid> _merge;
    private readonly Func<TMonoid, int, TMonoid> _appendNode;

    public ReRooting(Func<TMonoid, TMonoid, TMonoid> merge,
        Func<TMonoid, int, TMonoid> appendNode,
        TMonoid identity) {
        _merge = merge;
        _appendNode = appendNode;
        _identity = identity;
    }

    public TMonoid[] Solve(List<int>[] adj, int root = 0) {
        var n = adj.Length;
        var ans = new TMonoid[n];
        var parents = new int[n];
        parents[root] = -1;
        var permutation = new List<int>();
        var visited = new bool[n];
        var stack = new Stack<int>();
        stack.Push(root);
        while (stack.Count > 0) {
            var current = stack.Pop();
            if (visited[current]) continue;
            visited[current] = true;
            permutation.Add(current);
            foreach (var child in adj[current]) {
                if (!visited[child]) {
                    parents[child] = current;
                    stack.Push(child);
                }
            }
        }
        var dp = new TMonoid[n];
        foreach (var p in permutation.AsEnumerable().Reverse()) {
            var val = _identity;
            foreach (var child in adj[p]) {
                if (child == parents[p]) continue;
                val = _merge(val, dp[child]);
            }
            dp[p] = _appendNode(val, p);
        }
        var fromParent = new TMonoid[n];
        var accumulateFromTail = new TMonoid[n + 1];
        var subTreeResult = new TMonoid[n];
        foreach (var p in permutation) {
            int count = adj[p].Count;
            var accumulate = _identity;
            if (count > 0) {
                for (int i = 0; i < count; i++) {
                    var child = adj[p][i];
                    subTreeResult[i] = child == parents[p] ? fromParent[p] : dp[child];
                }
                accumulateFromTail[count] = _identity;
                for (int i = count - 1; i >= 0; i--) {
                    accumulateFromTail[i] = _merge(subTreeResult[i], accumulateFromTail[i + 1]);
                }
                for (int i = 0; i < count; i++) {
                    var child = adj[p][i];
                    if (child != parents[p]) {
                        fromParent[child] = _appendNode(_merge(accumulate, accumulateFromTail[i + 1]), p);
                    }
                    accumulate = _merge(accumulate, subTreeResult[i]);
                }
            }
            ans[p] = _appendNode(accumulate, p);
        }
        return ans;
    }
}
internal partial class Solver : Scanner {
    static readonly int? StackSizeInMebiByte = null; //50;
    public static void StartAndJoin(Action action, int maxStackSize) {
        var thread = new Thread(new ThreadStart(action), maxStackSize);
        thread.Start();
        thread.Join();
    }

    public static void Main() {
#if LOCAL
        byte[] inputBuffer = new byte[1000000];
        var inputStream = Console.OpenStandardInput(inputBuffer.Length);
        using (var reader = new StreamReader(inputStream, Console.InputEncoding, false, inputBuffer.Length)) {
            Console.SetIn(reader);
            new Solver(Console.In, Console.Out).Run();
        }
#else
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        if (StackSizeInMebiByte.HasValue) {
            StartAndJoin(() => new Solver(Console.In, Console.Out).Run(), StackSizeInMebiByte.Value * 1024 * 1024);
        } else {
            new Solver(Console.In, Console.Out).Run();
        }
        Console.Out.Flush();
#endif
    }

#pragma warning disable IDE0052
    private readonly TextReader cin;
    private readonly TextWriter cout;
    private readonly TextWriter cerr;
#pragma warning restore IDE0052

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        cin = reader;
        cout = writer;
        cerr = Console.Error;
    }

    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

#pragma warning disable IDE1006
#pragma warning disable IDE0051
    private int ni() { return NextInt(); }
    private int[] ni(int n) { return NextIntArray(n); }
    private long nl() { return NextLong(); }
    private long[] nl(int n) { return NextLongArray(n); }
    private double nd() { return NextDouble(); }
    private double[] nd(int n) { return NextDoubleArray(n); }
    private string ns() { return Next(); }
    private string[] ns(int n) { return NextArray(n); }
#pragma warning restore IDE1006
#pragma warning restore IDE0051
}

#if DEBUG
internal static class LinqPadExtension {
    public static string TextDump<T>(this T obj) {
        if (obj is IEnumerable) return (obj as IEnumerable).Cast<object>().JoinToString().Dump();
        else return obj.ToString().Dump();
    }
    public static T Dump<T>(this T obj) {
        return LINQPad.Extensions.Dump(obj);
    }
}
#endif

public class Scanner {
    private readonly TextReader Reader;
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    private readonly char[] buffer = new char[2 * 1024];
    private int cursor = 0, length = 0;
    private string Token;
    private readonly StringBuilder sb = new StringBuilder(1024);

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        Reader = reader;
    }

    public int NextInt() { return checked((int)NextLong()); }
    public long NextLong() {
        var s = Next();
        long r = 0;
        int i = 0;
        bool negative = false;
        if (s[i] == '-') {
            negative = true;
            i++;
        }
        for (; i < s.Length; i++) {
            r = r * 10 + (s[i] - '0');
#if DEBUG
            if (!char.IsDigit(s[i])) throw new FormatException();
#endif
        }
        return negative ? -r : r;
    }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        string[] array = new string[size];
        for (int i = 0; i < size; i++) {
            array[i] = Next();
        }

        return array;
    }
    public int[] NextIntArray(int size) {
        int[] array = new int[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextInt();
        }

        return array;
    }

    public long[] NextLongArray(int size) {
        long[] array = new long[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextLong();
        }

        return array;
    }

    public double[] NextDoubleArray(int size) {
        double[] array = new double[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextDouble();
        }

        return array;
    }

    public string Next() {
        if (Token == null) {
            if (!StockToken()) {
                throw new Exception();
            }
        }
        var token = Token;
        Token = null;
        return token;
    }

    public bool HasNext() {
        if (Token != null) {
            return true;
        }

        return StockToken();
    }

    private bool StockToken() {
        while (true) {
            sb.Clear();
            while (true) {
                if (cursor >= length) {
                    cursor = 0;
                    if ((length = Reader.Read(buffer, 0, buffer.Length)) <= 0) {
                        break;
                    }
                }
                var c = buffer[cursor++];
                if (33 <= c && c <= 126) {
                    sb.Append(c);
                } else {
                    if (sb.Length > 0) break;
                }
            }

            if (sb.Length > 0) {
                Token = sb.ToString();
                return true;
            }

            return false;
        }
    }
}

Measured memory_bytes: 47316