/*

This Submission is to determine how many 120/240 min const. delivery point there are.

//info
120 req. steps <= 5
*/
#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream>
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>
#include <cstdlib>
#include <complex>
#include <cctype>
#include <bitset>
using namespace std;
typedef string::const_iterator State;
#define Ma_PI 3.141592653589793
#define eps 1e-5
#define LONG_INF 1e18
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007LL
#define MOD 998244353LL
#define seg_size 262144*4
#define REP(a,b) for(long long a = 0;a < b;++a)

unsigned long xor128() {
	static unsigned long x = time(NULL), y = 362436069, z = 521288629, w = 88675123;
	unsigned long t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
double dot(complex<double> a, complex<double> b) {
	return a.real() * b.real() + a.imag() * b.imag();
}
double gyaku_dot(complex<double> a, complex<double> b) {
	return a.real() * b.imag() - a.imag() * b.real();
}
double leng(complex<double> a) {
	return sqrt(a.real() * a.real() + a.imag() * a.imag());
}
double angles(complex<double> a, complex<double> b) {
	double cosine = dot(a, b) / (leng(a) * leng(b));
	double sine = gyaku_dot(a, b) / (leng(a) * leng(b));
	double kaku = acos(min((double)1.0, max((double)-1.0, cosine)));
	if (sine <= 0) {
		kaku = 2 * Ma_PI - kaku;
	}
	return kaku;
}
vector<int> convex_hull(vector<complex<double>> a) {
	vector<int> ans;
	double now_minnest = a[0].real();
	int now_itr = 0;
	REP(i, a.size()) {
		if (now_minnest > a[i].real()) {
			now_minnest = a[i].real();
			now_itr = i;
		}
	}
	ans.push_back(now_itr);
	complex<double> ba(0, 1);
	while (true) {
		int now_go = 0;
		double now_min = 0;
		double now_length = 0;
		int starter = ans[ans.size() - 1];
		for (int i = 0; i < a.size(); ++i) {
			if (i != starter) {
				double goa = angles(ba, a[i] - a[starter]);
				if (goa - now_min >= eps || (abs(goa - now_min) <= eps && (abs(a[i] - a[starter]) - now_length) >= eps)) {
					now_min = goa;
					now_go = i;
					now_length = abs(a[i] - a[starter]);
				}
			}
		}
		if (now_go == ans[0]) break;
		ans.push_back(now_go);
		ba = complex<double>(a[now_go] - a[starter]);
	}
	return ans;
}
string s;
vector<int> vertexs[200000];
int cnt[200000];
int distances[200000];
void dfs(int now, int back) {
	REP(q, vertexs[now].size()) {
		if (vertexs[now][q] == back) continue;
		if (cnt[vertexs[now][q]] == 0) continue;
		distances[vertexs[now][q]] = distances[now];
		if (s[vertexs[now][q]] == 'W') distances[vertexs[now][q]] += 2;
		dfs(vertexs[now][q], now);
	}
}
int main() {
	iostream::sync_with_stdio(false);
	cin.tie(0);
	int n;
	cin >> n;
	REP(i, n - 1) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		vertexs[a].push_back(b);
		vertexs[b].push_back(a);
		cnt[a]++;
		cnt[b]++;
	}
	cin >> s;
	int hoge = 0;
	for (int i = 0; i < s.length(); ++i) {
		if (s[i] == 'W')hoge++;
	}
	if (hoge <= 1) {
		cout << hoge << endl;
		return 0;
	}
	queue<int> next;
	for (int i = 0; i < n; ++i) {
		if (cnt[i] == 1&&s[i] == 'B') {
			next.push(i);
		}
	}
	while (next.empty() == false) {
		int now = next.front(); next.pop();
		cnt[now] = 0;
		REP(i, vertexs[now].size()) {
			cnt[vertexs[now][i]]--;
			cnt[vertexs[now][i]] = max(cnt[vertexs[now][i]], 0);
			if (s[vertexs[now][i]] == 'B'&&cnt[vertexs[now][i]] == 1) {
				next.push(vertexs[now][i]);
			}
		}
	}
	int ans = 0;
	for (int i = 0; i < n; ++i) {
		if (cnt[i] != 0) {
			int cnter = 0;
			if (s[i] == 'W')cnter++;
			REP(q, vertexs[i].size()) {
				if (cnt[vertexs[i][q]] != 0) {
					cnter++;
					ans++;
				}
			}
			ans += cnter % 2;
			if (cnter % 2 == 0) {
				s[i] = 'B';
			}
			else {
				s[i] = 'W';
			}
		}
	}
	REP(i, n) {
		if (cnt[i] != 0) {
			dfs(i, -1);
			break;
		}
	}
	int now_max = -1;
	int now_itr = 0;
	REP(i, n) {
		if (cnt[i] == 1) {
			if (now_max < distances[i]) {
				now_max = distances[i];
				now_itr = i;
			}
		}
		distances[i] = 0;
	}
	if (s[now_itr] == 'W') {
		distances[now_itr] = 2;
	}
	dfs(now_itr, -1);
	now_max = 0;
	REP(q, n) {
		if (cnt[q] != 0) {
			now_max = max(now_max, distances[q]);
		}
	}
	cout << ans-now_max << endl;
}

Measured memory_bytes: 15936