#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
const int INF = 1e10;
const int MOD = 1e9 + 7;
#define dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
#define pb push_back
#define mp make_pair
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define itn int
bool dbg = false;
string C;
template <typename sum_t, typename key_t>
struct ReRooting {
    struct Edge {
        int to;
        key_t data;
        sum_t dp, ndp;
    };

    using F = function<sum_t(sum_t, sum_t)>;
    using G = function<sum_t(sum_t, key_t)>;

    vector<vector<Edge>> g;
    vector<sum_t> subdp, dp;
    const sum_t ident;
    const F f;
    const G gg;

    ReRooting(int V, const F f, const G g, const sum_t& ident)
        : g(V), f(f), gg(g), ident(ident), subdp(V, ident), dp(V, ident) {}

    void add_edge(int u, int v, const key_t& d) {
        g[u].emplace_back((Edge){v, d, ident, ident});
        g[v].emplace_back((Edge){u, d, ident, ident});
    }

    void add_edge_bi(int u, int v, const key_t& d, const key_t& e) {
        g[u].emplace_back((Edge){v, d, ident, ident});
        g[v].emplace_back((Edge){u, e, ident, ident});
    }

    void dfs_sub(int idx, int par) {
        for (auto& e : g[idx]) {
            if (e.to == par)
                continue;
            dfs_sub(e.to, idx);
            subdp[idx] = f(subdp[idx], gg(subdp[e.to], e.to));
        }
    }

    void dfs_all(int idx, int par, const sum_t& top) {
        sum_t buff{ident};
        for (int i = 0; i < (int)g[idx].size(); i++) {
            auto& e = g[idx][i];
            e.ndp = buff;
            e.dp = gg(par == e.to ? top : subdp[e.to], e.to);
            buff = f(buff, e.dp);
        }
        dp[idx] = buff;
        buff = ident;
        for (int i = (int)g[idx].size() - 1; i >= 0; i--) {
            auto& e = g[idx][i];
            if (e.to != par)
                dfs_all(e.to, idx, f(e.ndp, buff));
            e.ndp = f(e.ndp, buff);
            buff = f(buff, e.dp);
        }
    }

    vector<sum_t> build(int start) {
        dfs_sub(start, -1);
        dfs_all(start, -1, ident);
        return dp;
    }
};
//https://ei1333.hateblo.jp/entry/2018/12/21/004022

int N;
int x[101010], y[101010];
bool no_use[101010];

vector<vector<int>> G_origin;
int G_deg[101010];

vector<vector<int>> G;

void kezuru() {
    queue<int> que;
    FOR(N) {
        if (G_origin[i].size() == 1 && C[i] == 0)
            que.push(i);
        G_deg[i] = G_origin[i].size();
    }
    while (!que.empty()) {
        int a = que.front();
        que.pop();
        no_use[a] = 1;
        if (C[a] == 0) {
            for (auto& to : G_origin[a]) {
                if (no_use[to])
                    continue;
                G_deg[to]--;
                if (C[to] == 0 && G_deg[to] == 1) {
                    que.push(to);
                }
            }
        }
    }
    FOR(a, N) {
        for (auto& b : G_origin[a]) {
            if (no_use[a] == 0 && no_use[b] == 0) {
                G[a].pb(b);
                G[b].pb(a);
            }
        }
    }
}

struct node {
    itn x_time;
    int x_flag;
    int y_time;
    int y_flag;
};

void solve() {

    int flag_W = 0;
    FOR(N)
    chmax(flag_W, (int)C[i]);

    if (!flag_W) {
        cout << 0 << endl;
        return;
    }

    G_origin.resize(N);
    G.resize(N);

    FOR(N - 1) {
        G_origin[x[i]].pb(y[i]);
        G_origin[y[i]].pb(x[i]);
    }

    //黒い葉とかを削る
    kezuru();

    auto f1 = [](node a, node b) {
        if (a.x_time + b.y_time < a.y_time + b.x_time) {
            return node{
                a.x_time + b.x_time,
                a.x_flag ^ b.x_flag,
                a.x_time + b.y_time,
                a.x_flag ^ b.y_flag};
        } else {
            return node{
                a.x_time + b.x_time,
                a.x_flag ^ b.x_flag,
                a.y_time + b.x_time,
                a.y_flag ^ b.x_flag};
        }
    };
    auto f2 = [&](node a, int idx) {
        return node{
            a.x_time + 2 + (a.x_flag ^ (!C[idx])),
            1,
            a.y_time + 1 + (a.y_flag ^ (!C[idx])),
            0};
    };
    node e{0, 0, 0, 0};

    ReRooting<node, int> tree(N, f1, f2, e);
    FOR(N - 1) {
        if (!no_use[x[i]] && !no_use[y[i]])

            tree.add_edge(x[i], y[i], 0);
    }

    int start;
    FOR(N) {
        if (!no_use[i])
            start = i;
    }

    itn ans = INF;
    auto dp = tree.build(start);
    FOR(N) {
        if (!no_use[i]) {
            cerr << i + 1 << " : " << dp[i].y_time << " " << dp[i].y_flag << " : " << dp[i].y_time + (dp[i].y_flag ^ (int)C[i]) << endl;
            chmin(ans, dp[i].y_time + (dp[i].y_flag ^ (int)C[i]));
            chmin(ans, dp[i].x_time + (dp[i].x_flag ^ (int)C[i]));
        }
    }
    cout << ans << endl;
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> N;
    FOR(N - 1) {
        cin >> x[i] >> y[i];
        x[i]--;
        y[i]--;
    }
    cin >> C;
    for (auto& c : C)
        if (c == 'W')
            c = 1;
        else
            c = 0;


    solve();
    return 0;
}


Measured memory_bytes: 96076