//start of jonathanirvings' template v3.0.3 (BETA)

#include <bits/stdc++.h>
using namespace std;

typedef long long LL;
typedef pair<int,int> pii;
typedef pair<LL,LL> pll;
typedef pair<string,string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<LL> vl;
typedef vector<vl> vvl;

double EPS = 1e-9;
int INF = 1000000005;
long long INFF = 1000000000000000005LL;
double PI = acos(-1);
int dirx[8] = {-1,0,0,1,-1,-1,1,1};
int diry[8] = {0,1,-1,0,-1,1,-1,1};

#ifdef TESTING
  #define DEBUG fprintf(stderr,"====TESTING====\n")
  #define VALUE(x) cerr << "The value of " << #x << " is " << x << endl
  #define debug(...) fprintf(stderr, __VA_ARGS__)
#else
  #define DEBUG 
  #define VALUE(x)
  #define debug(...)
#endif

#define FOR(a,b,c) for (int (a)=(b);(a)<(c);++(a))
#define FORN(a,b,c) for (int (a)=(b);(a)<=(c);++(a))
#define FORD(a,b,c) for (int (a)=(b);(a)>=(c);--(a))
#define FORSQ(a,b,c) for (int (a)=(b);(a)*(a)<=(c);++(a))
#define FORC(a,b,c) for (char (a)=(b);(a)<=(c);++(a))
#define FOREACH(a,b) for (auto &(a) : (b))
#define REP(i,n) FOR(i,0,n)
#define REPN(i,n) FORN(i,1,n)
#define MAX(a,b) a = max(a,b)
#define MIN(a,b) a = min(a,b)
#define SQR(x) ((LL)(x) * (x))
#define RESET(a,b) memset(a,b,sizeof(a))
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ALL(v) v.begin(),v.end()
#define ALLA(arr,sz) arr,arr+sz
#define SIZE(v) (int)v.size()
#define SORT(v) sort(ALL(v))
#define REVERSE(v) reverse(ALL(v))
#define SORTA(arr,sz) sort(ALLA(arr,sz))
#define REVERSEA(arr,sz) reverse(ALLA(arr,sz))
#define PERMUTE next_permutation
#define TC(t) while(t--)

inline string IntToString(LL a){
  char x[100];
  sprintf(x,"%lld",a); string s = x;
  return s;
}

inline LL StringToInt(string a){
  char x[100]; LL res;
  strcpy(x,a.c_str()); sscanf(x,"%lld",&res);
  return res;
}

inline string GetString(void){
  char x[1000005];
  scanf("%s",x); string s = x;
  return s;
}

inline string uppercase(string s){
  int n = SIZE(s); 
  REP(i,n) if (s[i] >= 'a' && s[i] <= 'z') s[i] = s[i] - 'a' + 'A';
  return s;
}

inline string lowercase(string s){
  int n = SIZE(s); 
  REP(i,n) if (s[i] >= 'A' && s[i] <= 'Z') s[i] = s[i] - 'A' + 'a';
  return s;
}

inline void OPEN (string s) {
  #ifndef TESTING
  freopen ((s + ".in").c_str (), "r", stdin);
  freopen ((s + ".out").c_str (), "w", stdout);
  #endif
}

//end of jonathanirvings' template v3.0.3 (BETA)

unordered_map<int,int> dp[100005][3];
vi adj[100005];
vi child[100005];
int ada[100005];
int parent[100005];
string s;
int n,a,b;

vii dp2[100005];
int cnt2[100005];
bool dah2[100005];
int tot2[100005];

void dfs(int now,int pt)
{
  parent[now] = pt;
  ada[now] = s[now] == 'W' ? 1 : 0;
  REP(i,SIZE(adj[now]))
  {
    if (adj[now][i] == pt) continue;
    child[now].pb(adj[now][i]);
    dfs(adj[now][i],now);
    ada[now] += ada[adj[now][i]];
  }
}

int jahja(int now,int st,int pre);

void jahja2(int now)
{
  if (dah2[now]) return;
  dah2[now] = 1;
  for (int x : adj[now])
  {
    if (x == parent[now]) continue;
    if (jahja(x,0,now) == 0) continue;
    ++cnt2[now];
    dp2[now].pb(mp(jahja(x,1,now) - jahja(x,0,now),x));
    tot2[now] += jahja(x,0,now);
  }
  SORT(dp2[now]);
  if (SIZE(dp2[now]) >= 5) dp2[now].resize(5);
}

int jahja(int now,int st,int pre)
{
  // debug("IN: %d %d %d\n",now,st,pre);
  // if (st == 1 && ada[now] == 1 && s[now] == 'W') return 2;
  if (st != 2) {
    int cnt = 0;
    if (pre == parent[now]) cnt = ada[now];
    else cnt = ada[0] - ada[pre];
    if (cnt == 0) return 0;
  }
  if (dp[now][st].count(pre)) return dp[now][st][pre];
  // int &ret = dp[now][st][pre];
  int cnt = 0;
  int ret = 0;
  // if (st == 2)
  // {
  //   for (int x : child[now])
  //   {
  //     if (ada[x] == ada[now]) return ret = jahja(x,2);
  //   } 
  //   if (s[now] == 'W')
  //   {
  //     for (int x : child[now])
  //     {
  //       if (ada[x] + 1 == ada[now])
  //       {
  //         MIN(ret,jahja(x,2));
  //         return ret;
  //       }
  //     } 
  //   }
  // }
  
  jahja2(now);
  vii beda = dp2[now];
  cnt = cnt2[now];
  ret = tot2[now];

  if (pre != parent[now])
  {
    // kurangin pre
    if (pre != -1)
    {
      if (jahja(pre,0,now) != 0)
      {
        --cnt;
        ret -= jahja(pre,0,now);
        REP(i,SIZE(beda)) if(beda[i].se == pre)
        {
          beda.erase(beda.begin() + i);
          break;
        }
      }
    }
    if (parent[now] != -1)
    {
      // tambah parent[now]
      if (jahja(parent[now],0,now) != 0)
      {
        ++cnt;
        ret += jahja(parent[now],0,now);
        beda.pb(mp(jahja(parent[now],1,now) - jahja(parent[now],0,now),parent[now]));
      }
    }
    if (SIZE(beda) > 0) SORT(beda);
  }

  // for (int x : adj[now])
  // {
  //   if (x == pre) continue;
  //   if (jahja(x,0,now) == 0) continue;
  //   ++cnt;
  //   beda.pb(jahja(x,1,now) - jahja(x,0,now));
  //   ret += jahja(x,0,now);
  // }
  SORT(beda);
  if (st >= 1 && SIZE(beda) >= 1) ret += beda[0].fi;
  if (st >= 2 && SIZE(beda) >= 2) ret += beda[1].fi;
  if (st == 0)
  {
    if (s[now] == 'B') ++cnt;
    if (cnt % 2 == 1) ret += 3;
    else ret += 2;
  } else if (st == 1)
  {
    if (s[now] == 'B') ++cnt;
    if (SIZE(beda) >= 1) --cnt;
    if (cnt % 2 == 1) ret += 2;
    else ret += 1;
  } else if (st == 2)
  {
    if (s[now] == 'W') ++cnt;
    if (SIZE(beda) >= 1) --cnt;
    // if (SIZE(beda) >= 2) --scnt;
    if (SIZE(beda) >= 2) ++ret;
    if (cnt % 2 == 1) ret += 1;
    else ret += 0;
  }
  debug("OUT: %d %d %d %d\n",now,st,pre,ret);
  return dp[now][st][pre] = ret;
}

int main()
{
  scanf("%d",&n);
  REP(i,n-1)
  {
    scanf("%d %d",&a,&b);
    --a; --b;
    adj[a].pb(b);
    adj[b].pb(a);
  }
  s = GetString();
  dfs(0,-1);
  // REP(i,n) VALUE(ada[i]);
  // RESET(dp,-1);
  // REP(i,n) REP(j,3) dp[i][j].clear();
  int risan = INF;
  REP(i,n) MIN(risan,jahja(i,2,-1));
  printf("%d\n",risan);
  return 0;
}











Measured memory_bytes: 83840