const int N = 400005;
const int LG = 21;
const long long MOD = 1e9 + 7;
const long long INF = 1e9;

#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <cmath>
#include <time.h>
#include <unordered_set>
#include <bitset>
#include <deque>

using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<ll> vi;

#define forn(i, n) for (int (i) = 0; (i) != (n); (i)++)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define popcount(x) __builtin_popcount(x)
#define popcountll(x) __builtin_popcountll(x)
#define fi first
#define se second
#define re return
#define uniq(x) sort(all(x)); (x).resize(unique(all(x)) - (x).begin())

#ifdef LOCAL
#define dbg(x) cerr << __LINE__ << " " << #x << " " << x << endl
#define ln cerr << __LINE__ << endl
#else
#define dbg(x) void(0)
#define ln void(0)
#endif // LOCAL

int cx[4] = {-1, 0, 1, 0};
int cy[4] = {0, -1, 0, 1};

ll inq(ll x, ll y)
{
    if (!y) re 1 % MOD;
    ll l = inq(x, y / 2);
    if (y % 2) re l * l % MOD * x % MOD;
    re l * l % MOD;
}

ll rev(ll x)
{
    return inq(x, MOD - 2);
}

bool __precomputed_combinatorics = 0;
vector<ll> __fact, __ufact, __rev;

void __precompute_combinatorics()
{
    __precomputed_combinatorics = 1;
    __fact.resize(N);
    __ufact.resize(N);
    __rev.resize(N);
    __rev[1] = 1;
    for (int i = 2; i < N; i++) __rev[i] = MOD - __rev[MOD % i] * (MOD / i) % MOD;
    __fact[0] = 1, __ufact[0] = 1;
    for (int i = 1; i < N; i++) __fact[i] = __fact[i - 1] * i % MOD, __ufact[i] = __ufact[i - 1] * __rev[i] % MOD;
}

ll fact(int x)
{
    if (!__precomputed_combinatorics) __precompute_combinatorics();
    return __fact[x];
}

ll cnk(int n, int k)
{
    if (!__precomputed_combinatorics) __precompute_combinatorics();
    return __fact[n] * __ufact[n - k] % MOD * __ufact[k] % MOD;
}

void __fast_IO()
{
    #ifdef ONLINE_JUDGE
        ios_base::sync_with_stdio(false);
        cin.tie(0);
        cout.tie(0);
    #endif // ONLINE_JUDGE
}

//##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**
//##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**##**

int n;
vector<int> g[N], graph[N];
string s;
int exits[N];
int root = 0;
int cost[N];
int res;
int dp[N];

void dfs(int v, int p)
{
    if (s[v] == 'W') exits[v] = 1;
    for (auto u : g[v]) if (u != p)
    {
        dfs(u, v);
        if (exits[u]) exits[v] = 1;
    }
}

void dfs2(int v, int p)
{
    int mx1 = 0, mx2 = 0;
    for (auto u : graph[v]) if (u != p)
    {
        dfs2(u, v);
        if (dp[u] > mx2) mx2 = dp[u];
        if (mx2 > mx1) swap(mx1, mx2);
    }
    dp[v] = mx1 + cost[v];
    res = max(res, mx1 + cost[v] + mx2);
}

signed main()
{
    __fast_IO();
    cin >> n;
    for (int i = 0; i < n - 1; i++)
    {
        int a, b;
        cin >> a >> b;
        a--, b--;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    cin >> s;
    int cnt = 0;
    for (int i = 0; i < n; i++)
    {
        if (s[i] == 'W') cnt++;
    }
    if (cnt == 0) cout << "0", exit(0);
    if (cnt == 1) cout << "1", exit(0);
    for (int i = 0; i < n; i++)
    {
        if (s[i] == 'W')
        {
            root = i;
            break;
        }
    }
    dfs(root, -1);
    ll ans = 0;
    for (int i = 0; i < n; i++)
    {
        for (auto u : g[i])
        {
            if (exits[i] && exits[u]) graph[i].push_back(u), ans++;
        }
    }
    //cout << cnt << " " << ans << "\n";
    for (int i = 0; i < n; i++)
    {
        if (exits[i])
        {
            if (graph[i].size() % 2 == 1 && s[i] == 'B') ans += 1, cost[i] += 2;
            else if (graph[i].size() % 2 == 0 && s[i] == 'W') ans += 1, cost[i] += 2;
        }
        //cout << cost[i] << " ";
    }
    dfs2(root, -1);
    //cout << "\n";
    cout << ans - res << "\n";
}

/* Note:
Check constants at the beginning of the code.
N is set to 4e5 but be careful in problems with large constant factor.
Check corner cases.
No def int long long for now.
*/


Measured memory_bytes: 36224