#include <bits/stdc++.h>
using namespace std;
/*#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename T> using gpp_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T, typename L> using gpp_map = tree<T, L, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T> using gpp_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;*/
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin);i<(end);i++)
#define REP(i, n) FOR(i,0,n)
#define IFOR(i, begin, end) for(int i=(end)-1;i>=(begin);i--)
#define IREP(i, n) IFOR(i,0,n)
#define Sort(v) sort(v.begin(), v.end())
#define Reverse(v) reverse(v.begin(), v.end())
#define all(v) v.begin(),v.end()
#define SZ(v) ((int)v.size())
#define Lower_bound(v, x) distance(v.begin(), lower_bound(v.begin(), v.end(), x))
#define Upper_bound(v, x) distance(v.begin(), upper_bound(v.begin(), v.end(), x))
#define Max(a, b) a = max(a, b)
#define Min(a, b) a = min(a, b)
#define bit(n) (1LL<<(n))
#define bit_exist(x, n) ((x >> n) & 1)
#define debug(x) cout << #x << "=" << x << endl;
#define vdebug(v) { cout << #v << "=" << endl; REP(i_debug, v.size()){ cout << v[i_debug] << ","; } cout << endl; }
#define mdebug(m) { cout << #m << "=" << endl; REP(i_debug, m.size()){ REP(j_debug, m[i_debug].size()){ cout << m[i_debug][j_debug] << ","; } cout << endl;} }
#define Return(ans) { cout << (ans) << endl; return 0; }
#define pb push_back
#define f first
#define s second
#define int long long
#define INF 1000000000000000000
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for (auto &x : v) is >> x; return is; }
template<typename T> ostream &operator<<(ostream &os, vector<T> &v){ for(int i = 0; i < v.size(); i++) { cout << v[i]; if(i != v.size() - 1) cout << endl; }; return os; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, pair<T1, T2> p){ cout << '(' << p.first << ',' << p.second << ')'; return os; }
template<typename T> void Out(T x) { cout << x << endl; }
template<typename T1, typename T2> void Ans(bool f, T1 y, T2 n) { if(f) Out(y); else Out(n); }

using vec = vector<int>;
using mat = vector<vec>;
using Pii = pair<int, int>;
using PiP = pair<int, Pii>;
using PPi = pair<Pii, int>;
using Pdi = pair<double, int>;
using bools = vector<bool>;
using pairs = vector<Pii>;

//int dx[4] = {1,0,-1,0};
//int dy[4] = {0,1,0,-1};
//char d[4] = {'D','R','U','L'};

const int mod = 1000000007;
//const int mod = 998244353;
//#define Add(x, y) x = (x + (y)) % mod
//#define Mult(x, y) x = (x * (y)) % mod

struct edge{int to, cost, id;};

class Graph
{
public:
    int N;
    vector<vector<edge>> G;
    string c;
    vec cnt, dp;
    int L = 0, D = 0;
    bools rev;

    Graph(int N): N(N){
        G = vector<vector<edge>>(N, vector<edge>(0));
        cnt = vec(N, 0);
        rev = bools(N, false);
        dp = vec(N, 0);
    }

    void add_Directed_edge(int from, int to, int cost = 1, int id = 0){
        G[from].push_back(edge({to, cost, id}));
    }

    void add_Undirected_edge(int v1, int v2, int cost = 1, int id = 0){
        add_Directed_edge(v1, v2, cost, id);
        add_Directed_edge(v2, v1, cost, id);
    }

    void dfs1(int v, int p = -1){
        if(c[v] == 'W') cnt[v]++;
        rev[v] = (p != -1);
        for(auto e: G[v]) if(e.to != p){
            dfs1(e.to, v);
            cnt[v] += cnt[e.to];
            if(cnt[e.to]){
                L += 2;
                rev[v] = !rev[v];
            }
        }

        if(rev[v]){
            if(c[v] == 'W') c[v] = 'B';
            else c[v] = 'W';
        }
        
        if(cnt[v] && c[v] == 'W') L++;
    }

    void dfs2(int v, int p = -1){
        vec t;
        for(auto e: G[v]) if(e.to != p && cnt[e.to]){
            dfs2(e.to, v);
            t.pb(dp[e.to]);
            Max(dp[v], dp[e.to]);
        }

        if(c[v] == 'W') dp[v]++;

        if(SZ(t) >= 2){
            Sort(t); Reverse(t);
            int s = t[0] + t[1];
            if(c[v] == 'W') s++;
            Max(D, s);
        }

        Max(D, dp[v]);
    }

};

signed main(){

    int N; cin >> N;
    Graph G(N);
    REP(i, N - 1){
        int x, y; cin >> x >> y;
        G.add_Undirected_edge(x - 1, y - 1);
    }
    string c; cin >> c;
    G.c = c;

    int r = -1, nW = 0;
    REP(i, N) if(c[i] == 'W'){
        r = i;
        nW++;
    }
    if(r == -1){
        Out(0);
        return 0;
    }
    if(nW == 1){
        Out(1);
        return 0;
    }

    G.dfs1(r);
    G.dfs2(r);
    
    int ans = G.L - G.D * 2;
    Out(ans);

    return 0;
}


Measured memory_bytes: 20428