///////////////////////////////////////////////////////////////////////////////

#include <bits/stdc++.h>
#include <unistd.h>
#include <time.h>
#include <sys/time.h>

using namespace std;

///////////////////////////////////////////////////////////////////////////////

#define DEBUG 0

#define pb push_back
#define V vector
#define M unordered_map
#define S static

#define rep(i,n) for(ll i=0LL; i<n; ++i)
#define srep(i,s,n) for(ll i=s; i<n; ++i)
#define rrep(i,n) for(ll i=n-1LL; i>=0LL; --i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define CIN(x) do { \
        assert(!cin.eof()); \
        cin >> x; \
        assert(!cin.fail()); \
} while(0);
#if DEBUG
#define debug_print(...) _debug_print(__VA_ARGS__)
#define debug_printf(...) printf(__VA_ARGS__)
#define debug_print_time _debug_print_time
#else // DEBUG
#define debug_print(...)
#define debug_printf(...)
#define debug_print_time
#endif // DEBUG

typedef long long ll;
typedef unsigned long long ull;
typedef tuple<ll, ll> t2;
typedef tuple<ll, ll, ll> t3;
typedef tuple<ll, ll, ll, ll> t4;
typedef tuple<ll, ll, ll, ll, ll> t5;
template <typename T>
using priority_queue_incr = priority_queue<T, V<T>, greater<T> >;

///////////////////////////////////////////////////////////////////////////////

template <typename TT, typename T>
T get_m(M<TT, T> &m, TT k, T default_value)
{
    if (m.find(k) == m.end()) return m[k] = default_value;
    return m[k];
}

template <typename TT, typename T>
void incr_m(M<TT, T> &m, TT k)
{
    if (m.find(k) == m.end()) m[k] = 0;
    m[k]++;
}

template <typename TT, typename T>
void incr_m(map<TT, T> &m, TT k)
{
    if (m.find(k) == m.end()) m[k] = 0;
    m[k]++;
}

void llin(ll &a)
{
    CIN(a);
}

void llinl1(V<ll> &v, ll count)
{
    for (ll i = 0LL; i < count; ++i) {
        ll a;
        CIN(a);
        v.push_back(a);
    }
}

void llinl2(V<t2> &v, ll count)
{
    for (ll i = 0LL; i < count; ++i) {
        ll a, b;
        CIN(a >> b);
        v.push_back(t2(a, b));
    }
}

void llinl3(V<t3> &v, ll count)
{
    for (ll i = 0LL; i < count; ++i) {
        ll a, b, c;
        CIN(a >> b >> c);
        v.push_back(t3(a, b, c));
    }
}

void llinl4(V<t4> &v, ll count)
{
    for (ll i = 0LL; i < count; ++i) {
        ll a, b, c, d;
        CIN(a >> b >> c >> d);
        v.push_back(t4(a, b, c, d));
    }
}

void llina(V<ll> &v, ll count)
{
    llinl1(v, count);
}

template <typename T>
void sort(V<T> &v)
{
    sort(v.begin(), v.end());
}

template <typename T>
void sort_reverse(V<T> &v)
{
    sort(v.begin(), v.end(), greater<T>());
}

template <typename T>
void _debug_print(T x)
{
    cout << x << endl;
}

void _debug_print(const t2 &x)
{
    ll x1 = get<0>(x);
    ll x2 = get<1>(x);
    cout << "-- " << x1 << " -- " << x2 << endl;
}

void _debug_print(const t3 &x)
{
    ll x1 = get<0>(x);
    ll x2 = get<1>(x);
    ll x3 = get<2>(x);
    cout << "-- " << x1 << " -- " << x2 << " -- " << x3 << endl;
}

void _debug_print(const t4 &x)
{
    ll x1 = get<0>(x);
    ll x2 = get<1>(x);
    ll x3 = get<2>(x);
    ll x4 = get<3>(x);
    cout << "-- " << x1 << " -- " << x2
         << " -- " << x3 << " -- " << x4 << endl;
}

template <typename T>
void _debug_print(T xarray[], ll n)
{
    rep (i, n) _debug_print(xarray[i]);
}

template <typename T>
void _debug_print(const V<T> &xlist)
{
    for (auto x : xlist) {
        cout << "-- ";
        _debug_print(x);
    }
}

template <typename T>
void _debug_print(const set<T> &xset)
{
    for (auto x : xset) {
        cout << "-- ";
        _debug_print(x);
    }
}

template <typename TT, typename T>
void _debug_print(const M<TT, T> &xlist)
{
    for (auto x : xlist) {
        TT k = x.first;
        T v = x.second;
        cout << "====" << endl;
        cout << "K=";
        _debug_print(k);
        cout << "V=";
        _debug_print(v);
    }
}

template <typename TT, typename T>
void _debug_print(const map<TT, T> &xlist)
{
    for (auto x : xlist) {
        TT k = x.first;
        T v = x.second;
        cout << "====" << endl;
        cout << "K=";
        _debug_print(k);
        cout << "V=";
        _debug_print(v);
    }
}

void _debug_print_time(const char *prefix)
{
    struct timeval tv;
    gettimeofday(&tv, NULL);
#if DEBUG
    struct tm *tm = localtime(&tv.tv_sec);
#endif
    debug_printf("-- %s %02d:%02d:%02d.%06ld\n",
                  prefix, tm->tm_hour, tm->tm_min, tm->tm_sec, tv.tv_usec);
}

///////////////////////////////////////////////////////////////////////////////

void _main();
int main()
{
    cout << setprecision(12);
#if !DEBUG
    ios::sync_with_stdio(false);
    cin.tie(0);
#endif

    _main();
    return 0;
}

void make_edgelist(const V<t2> &srclist, V<ll> edgelist[])
{
    for (auto src : srclist) {
        ll a = get<0>(src);
        ll b = get<1>(src);
        edgelist[a].pb(b);
        edgelist[b].pb(a);
    }
}

ll cnt_w(const string &colors)
{
    ll ret = 0;
    for (auto c : colors) {
        if (c == 'W') ret++;
    }
    return ret;
}

void f_longest(ll &ev, ll &ecost, const V<ll> edgelist[],
                const ll digs[], const string &colors, ll n, ll sv)
{
    queue<ll> q;
    ll costs[100005];
    rep (i, 100005) costs[i] = -1;

    ecost = 0;

    costs[sv] = 0;
    q.push(sv);

    while (q.size()) {
        ll v = q.front(); q.pop();

        if (costs[v] >= ecost && digs[v] == 1) {
            ecost = costs[v];
            ev = v;
        }

        for (auto nv : edgelist[v]) {
            if (costs[nv] >= 0) continue;
            costs[nv] = costs[v];
            if ((digs[nv] & 1LL) && colors[nv] == 'B') costs[nv] += 2LL;
            if (!(digs[nv] & 1LL) && colors[nv] == 'W') costs[nv] += 2LL;
            q.push(nv);
        }
    }

    debug_printf("sv=%lld ev=%lld ecost=%lld\n", sv, ev, ecost);
}

void _main()
{
    ll n; llin(n);
    S V<t2> xylist; llinl2(xylist, n-1);
    S string colors; CIN(colors);

    if (cnt_w(colors) <= 1) {
        cout << cnt_w(colors) << endl;
        return;
    }

    colors = '_' + colors;

    S V<ll> edgelist_orig[100005];
    make_edgelist(xylist, edgelist_orig);

    S ll digs_old[100005];
    srep (v, 1, n+1) digs_old[v] = edgelist_orig[v].size();

    S queue<ll> q;
    S bool removed[100005] = {};
    srep (v, 1, n+1) {
        if (colors[v] == 'W') continue;
        if (digs_old[v] > 1) continue;
        q.push(v);
        removed[v] = true;
    }

    while (q.size()) {
        ll v = q.front(); q.pop();
        for (auto nv : edgelist_orig[v]) {
            if (removed[nv]) continue;
            digs_old[nv]--;
            if (colors[nv] == 'W') continue;
            if (digs_old[nv] > 1) continue;
            q.push(nv);
            removed[nv] = true;
        }
    }

    debug_printf("---- removed\n");
    debug_print(removed, n+1);

    S V<ll> edgelist[100005];
    S set<ll> new_vs;
    for (auto xy : xylist) {
        ll x = get<0>(xy);
        ll y = get<1>(xy);
        if (removed[x]) continue;
        if (removed[y]) continue;
        edgelist[x].pb(y);
        edgelist[y].pb(x);
        new_vs.insert(x);
        new_vs.insert(y);
    }

    S ll digs[100005] = {};
    for (auto v : new_vs) {
        digs[v] = edgelist[v].size();
    }

    ll sv = -1;
    for (auto v : new_vs) {
        if (digs[v] == 1) {
            sv = v;
            break;
        }
    }
    assert(sv > 0);

    ll ans = (new_vs.size()-1LL) * 2LL;
    for (auto v : new_vs) {
        if ((digs[v] & 1LL) && colors[v] == 'B') ans++;
        if (!(digs[v] & 1LL) && colors[v] == 'W') ans++;
    }

    ll ev, cost;
    f_longest(ev, cost, edgelist, digs, colors, n, sv);
    f_longest(ev, cost, edgelist, digs, colors, n, ev);
    debug_printf("after f_longest ans=%lld ev=%lld cost=%lld\n", ans, ev, cost);

    ans -= cost;

    debug_printf("---- ans\n");
    cout << ans << endl;
}

///////////////////////////////////////////////////////////////////////////////


Measured memory_bytes: 25220