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

#define int long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define reps(i, n) for (int i = 1; i <= (n); i++)
#define all(x) (x).begin(), (x).end()
#define uniq(x) (x).erase(unique(all(x)), end(x))
#define bit(n) (1LL << (n))
#define cdiv(a, b) (((a) - 1) / (b) + 1)
#define dump(x) cerr << #x " = " << (x) << endl
using vint = vector<int>;
using vvint = vector<vint>;
using pint = pair<int, int>;
using vpint = vector<pint>;
template<typename T> using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr int DY[8] = {0, 1, 0, -1, 1, 1, -1, -1};
constexpr int DX[8] = {1, 0, -1, 0, 1, -1, -1, 1};
int gcd(int a, int b) {
    while (b) { swap(a %= b, b); }
    return a;
}
int lcm(int a, int b) { return a / gcd(a, b) * b; }
template<typename T> void fin(T mes) {
    cout << mes << endl;
    exit(0);
}
template<typename T, typename U> bool chmax(T &a, const U &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> bool chmin(T &a, const U &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
template<typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
    os << "(" << rhs.first << ", " << rhs.second << ")";
    return os;
}
template<typename T> ostream &operator<<(ostream &os, const vector<T> &rhs) {
    os << "{";
    for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
        os << *itr << (next(itr) != rhs.end() ? ", " : "");
    }
    os << "}";
    return os;
}
struct setup {
    static constexpr int PREC = 20;
    setup() {
        cout << fixed << setprecision(PREC);
        cerr << fixed << setprecision(PREC);
    };
} setup;

int N;
int x[110000], y[110000];
int deg[110000];
string c;
vvint normed;
int bonus = 0;
int dfs(int cur, int par) {
    vint bs;
    rep(i, normed[cur].size()) {
        if (normed[cur][i] == par) { continue; }
        bs.push_back(dfs(normed[cur][i], cur) + 1);
    }
    sort(all(bs)), reverse(all(bs));
    int p = ((deg[cur] & 1) ^ (c[cur] == 'W')) - ((deg[cur] & 1) ^ (c[cur] == 'B'));
    if (bs.size() >= 2) { chmax(bonus, bs[0] + bs[1] + p + 1); }
    if (bs.empty()) { return p; }
    return bs[0] + p;
}
signed main() {
    cin >> N;
    vvint G(N);
    rep(i, N - 1) {
        cin >> x[i] >> y[i];
        x[i]--, y[i]--;
        G[x[i]].push_back(y[i]), G[y[i]].push_back(x[i]);
        deg[x[i]]++, deg[y[i]]++;
    }
    cin >> c;
    vint removed;
    rep(i, N) { if (deg[i] == 1 && c[i] == 'B') { removed.push_back(i); }}
    while (!removed.empty()) {
        int cur = removed.back();
        removed.pop_back();
        deg[cur] = 0;
        rep(i, G[cur].size()) {
            int k = G[cur][i];
            deg[k]--;
            if (deg[k] == 1 && c[k] == 'B') { removed.push_back(k); }
        }
    }
    rep(i,N)dump(deg[i]);
    int ans = 0;
    normed.resize(N);
    rep(i, N - 1) {
        if (deg[x[i]] <= 0 || deg[y[i]] <= 0) { continue; }
        normed[x[i]].push_back(y[i]), normed[y[i]].push_back(x[i]);
        ans += 2;
    }
    rep(i, N) { if (deg[i] > 0 && ((deg[i] & 1) ^ (c[i] == 'W'))) { ans++; }}
    int s = -1;
    rep(i, N) { if (deg[i] >= 2) { s = i; }}
    if (s == -1) { fin(count(all(c), 'W')); }
    dfs(s, -1);
    ans -= bonus;
    cout << ans << endl;
}

Measured memory_bytes: 22528