#include <bits/stdc++.h>
#define err(args...) {}
#ifdef DEBUG
#include "_debug.cpp"
#endif
using namespace std;
using ll = long long;
using ld = long double;
template <typename T> using lim = numeric_limits<T>;
template <typename T> istream& operator>>(istream& is, vector<T>& a) { for(T& x : a) { is >> x; } return is; }
template <typename X, typename Y> istream& operator>>(istream& is, pair<X, Y>& p) { return is >> p.first >> p.second; }
template <bool Directed, typename TEdge, bool Index> struct graph {
    using EType = TEdge;
    vector<TEdge> edges;
    vector<vector<int>> adj;
    graph(int n) : adj(n + Index) {}
    graph(int n, int m) : graph(n) { edges.reserve(m << not Directed); }
    TEdge& operator()(int e) { return edges[e]; }
    vector<int>& operator[](int u) { return adj[u]; }
    int size() { return adj.size() - Index; }
    void append(int u, const TEdge& e) {
        adj[u].push_back(edges.size());
        edges.push_back(e);
    }
    void add_edge(const TEdge& e) {
        append(e.u, e);
        if(not Directed) append(e.v, e.reverse());
    }
};
struct edge {
    int u, v;
    edge reverse() const { return {v, u}; }
    friend ostream& operator<<(ostream& os, const edge& e) {
        return os << "{u: " << e.u << ", v: " << e.v << "}";
    }
};
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    graph<0, edge, 1> g(n, n - 1);
    for(int i = 1; i < n; i++) {
        int u, v;
        cin >> u >> v;
        g.add_edge({u, v});
    }
    string c;
    cin >> c;
    c.insert(c.begin(), ' ');
    vector<int> degree(n + 1), degree_parity(n + 1);
    queue<int> q;
    for(int i = 1; i <= n; i++) {
        if((degree[i] = g[i].size()) == 1 and c[i] == 'B') {
            q.push(i);
        }
        degree_parity[i] = degree[i] & 1;
    }
    vector<bool> deleted(n + 1);
    deleted[0] = true;
    int edges = n - 1;
    while(not q.empty()) {
        int u = q.front();
        q.pop();
        deleted[u] = true;
        edges--;
        for(int e : g[u]) {
            degree_parity[g(e).v] ^= 1;
            if(--degree[g(e).v] == 1 and c[g(e).v] == 'B') {
                q.push(g(e).v);
            }
        }
    }
    if(count(deleted.begin(), deleted.end(), false) == 0) {
        cout << 0 << endl;
    } else if(count(deleted.begin(), deleted.end(), false) == 1) {
        cout << (c[find(deleted.begin(), deleted.end(), false) - deleted.begin()] == 'W') << endl;
    } else {
        auto flip_cost = [&](int i) {
            return (c[i] == 'W') ^ degree_parity[i];
        };
        auto farthest = [&](int s) -> pair<int, int> {
            vector<int> dist(n + 1, -1);
            priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q;
            q.push({dist[s] = 0, s});
            while(not q.empty()) {
                int d, u;
                tie(d, u) = q.top();
                q.pop();
                for(int e : g[u]) {
                    if(not deleted[g(e).v] and dist[g(e).v] == -1) {
                        q.push({dist[g(e).v] = d + 1 + flip_cost(g(e).v) - (flip_cost(g(e).v) ^ (degree[g(e).v] > 1)), g(e).v});
                    }
                }
            }
            return {max_element(dist.begin(), dist.end()) - dist.begin(), *max_element(dist.begin(), dist.end())};
        };
        int cost = -2;
        for(int i = 1; i <= n; i++) {
            if(not deleted[i]) {
                cost += flip_cost(i) + 2;
            }
        }
        cout << cost - farthest(farthest(find(deleted.begin(), deleted.end(), false) - deleted.begin()).first).second + 1 << endl;
    }
    return 0;
}

Measured memory_bytes: 10780