/*{{{*/
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<string>
#include<iostream>
#include<sstream>
#include<set>
#include<map>
#include<queue>
#include<bitset>
#include<vector>
#include<limits.h>
#include<assert.h>
#define SZ(X) ((int)(X).size())
#define ALL(X) (X).begin(), (X).end()
#define REP(I, N) for (int I = 0; I < (N); ++I)
#define REPP(I, A, B) for (int I = (A); I < (B); ++I)
#define FOR(I, A, B) for (int I = (A); I <= (B); ++I)
#define FORS(I, S) for (int I = 0; S[I]; ++I)
#define RS(X) scanf("%s", (X))
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#define CASET int ___T; scanf("%d", &___T); for(int cs=1;cs<=___T;cs++)
#define MP make_pair
#define PB push_back
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define LEN(X) strlen(X)
#define F first
#define S second
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
typedef long double LD;
typedef pair<int,int> PII;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef vector<PII> VPII;
typedef pair<LL,LL> PLL;
typedef vector<PLL> VPLL;
template<class T> void _R(T &x) { cin >> x; }
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%lld", &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template<class T, class... U> void R(T &head, U &... tail) { _R(head); R(tail...); }
template<class T> void _W(const T &x) { cout << x; }
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%lld", x); }
void _W(const double &x) { printf("%.16f", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template<class T,class U> void _W(const pair<T,U> &x) {_W(x.F); putchar(' '); _W(x.S);}
template<class T> void _W(const vector<T> &x) { for (auto i = x.begin(); i != x.end(); _W(*i++)) if (i != x.cbegin()) putchar(' '); }
void W() {}
template<class T, class... U> void W(const T &head, const U &... tail) { _W(head); putchar(sizeof...(tail) ? ' ' : '\n'); W(tail...); }
#ifdef HOME
 #define DEBUG(...) {printf("# ");printf(__VA_ARGS__);puts("");}
#else
 #define DEBUG(...)
#endif
int MOD = 1e9+7;
void ADD(LL& x,LL v){x=(x+v)%MOD;if(x<0)x+=MOD;}
/*}}}*/
const int SIZE = 1e6+10;
VI e[SIZE];
char s[SIZE];
int have_w[SIZE];
int bw[SIZE];
int base;
void dfs0(int x,int lt){
    if(s[x]=='W')have_w[x]=1;
    for(int y: e[x]){
        if(y==lt)continue;
        dfs0(y,x);
        if(have_w[y]){
            have_w[x]=1;
            base+=2;
            bw[x]^=1;
        }
    }
    if(x!=lt&&have_w[x])bw[x]^=1;
    if(!bw[x])base++;
}
int dp[SIZE][2];
int ans;
const int INF = 1e8;
void dfs(int x,int lt){
    dp[x][1]=-INF;
    dp[x][0]=-INF;
    for(int y:e[x]){
        if(y==lt)continue;
        if(!have_w[y])continue;
        dfs(y,x);
        ans=min(ans,base-dp[y][1]);
        ans=min(ans,base-dp[y][0]+bw[x]);
        ans=min(ans,base-dp[x][0]-dp[y][1]+(2*bw[x]-1));
        ans=min(ans,base-dp[x][1]-dp[y][0]+(2*bw[x]-1));
        REP(j,2)dp[x][j]=max(dp[x][j],dp[y][j]);
    }
    REP(i,2)dp[x][i]+=1-(2*bw[x]-1);
    dp[x][1]=max(dp[x][1],1-(2*bw[x]-1));
    dp[x][0]=max(dp[x][0],1);
}
int main(){
    int N; R(N);
    REPP(i,1,N){
        int x,y;
        R(x,y);
        e[x].PB(y);
        e[y].PB(x);
    }
    RS(s+1);
    int w_cnt=0;
    FOR(i,1,N){
        if(s[i]=='W')w_cnt++;
    }
    if(w_cnt <= 1){
        W(w_cnt);
        return 0;
    }
    int st;
    FOR(i,1,N){
        if(s[i]=='W'){
            st=i;
        }
        else bw[i]=1;
    }
    dfs0(st,st);
    ans=INF;
    dfs(st,st);
    W(ans);
    return 0;
}


Measured memory_bytes: 42240