#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned int uint;
typedef unsigned char uchar;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define REP(i,x) for(int i=0;i<(int)(x);i++)
#define REPS(i,x) for(int i=1;i<=(int)(x);i++)
#define RREP(i,x) for(int i=((int)(x)-1);i>=0;i--)
#define RREPS(i,x) for(int i=((int)(x));i>0;i--)
#define FOR(i,c) for(__typeof((c).begin())i=(c).begin();i!=(c).end();i++)
#define RFOR(i,c) for(__typeof((c).rbegin())i=(c).rbegin();i!=(c).rend();i++)
#define ALL(container) (container).begin(), (container).end()
#define RALL(container) (container).rbegin(), (container).rend()
#define SZ(container) ((int)container.size())
#define mp(a,b) make_pair(a, b)
#define pb push_back
#define eb emplace_back
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define __builtin_popcount __builtin_popcountll

template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
    os<<"["; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"]"; return os;
}
template<class T> ostream& operator<<(ostream &os, const set<T> &t) {
    os<<"{"; FOR(it,t) {if(it!=t.begin()) os<<","; os<<*it;} os<<"}"; return os;
}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}
template<class S, class T> pair<S,T> operator+(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first+t.first, s.second+t.second);}
template<class S, class T> pair<S,T> operator-(const pair<S,T> &s, const pair<S,T> &t){ return pair<S,T>(s.first-t.first, s.second-t.second);}

const int INF = 1<<28;
const double EPS = 1e-8;
const int MOD = 1000000007;

vector<vi> g;
string color;

// -1, invalid
// 0, internal
// 1 leaf
int state[100001];

pii visit(int p, int v, const vector<vi> &g) {
    pii r(0, v);
    for(int e : g[v]) {
        if (e != p && state[e] != -1) {
            pii t = visit(v, e, g);
            r = max(r, t);
        }
    }
    if ((color[v] == 'W') && (state[v] == 0)) {
        r.first += 2;
    }
    return r;
}
int diameter(const vector<vi> &g, int root) {
    pii r = visit(-1, root, g);
    pii t = visit(-1, r.second, g);
    return t.first; // (r.second, t.second) is farthest pair
}

// return if valid
bool dfs(int u, int p) {
    int valid_count = 0;
    for(int v : g[u]) {
        if (v != p) {
            valid_count += dfs(v, u);
        }
    }
    if (valid_count <= 0 + (p == -1)) {
        if (color[u] == 'B') state[u] = -1;
        else state[u] = 1;
    } else {
        state[u] = 0;
    }

    return state[u] != -1;
}

int n, m;
int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    cin >> n;
    g.resize(n);
    REP(i, n-1) {
        int u, v;
        cin >> u >> v; u--; v--;
        g[u].eb(v);
        g[v].eb(u);
    }
    cin >> color;

    if (count(ALL(color), 'W') == 1) {
        cout << 1 << endl;
        return 0;
    }

    if (color == string(n, 'B')) {
        cout << 0 << endl;
        return 0;
    }
    int root = -1;
    REP(i, n) if (color[i] == 'W') root = i;
    dfs(root, -1);
    int ans = 0;
    REP(i, n) {
        ans += (state[i] != -1) * 2;
    }
    ans -= 2;
    REP(i, n) {
        if (state[i] == 0) {
            int c = 0;
            for (int v : g[i]) c += state[v] != -1;
            if (c & 1) color[i] = (color[i] == 'W' ? 'B' : 'W');
        }
        ans += (state[i] == 0 && color[i] == 'W');
    }
    int d = diameter(g, root);
    ans -= d;
    cout << ans << endl;
    return 0;
}


Measured memory_bytes: 15696