# include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
typedef pair<LL, LL> pii;
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        sort(ALL((wpwpw)));(wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)

int n;
string s;
vector<int> g[101010];
int c, w, cntc[101010], cntw[101010];

LL ans = 0;

void dfs(int cur, int p){
    if(s[cur] == 'c')cntc[cur] = 1;
    if(s[cur] == 'w')cntw[cur] = 1;

    REP(i,(int)g[cur].size()){
        if(g[cur][i] == p)continue;
        dfs(g[cur][i], cur);
        cntc[cur] += cntc[g[cur][i]];
        cntw[cur] += cntw[g[cur][i]];
        if(s[cur] == 'w')ans += 1LL*cntc[g[cur][i]]*(w - 1 - cntw[g[cur][i]]);
    }
    if(p != -1 && s[cur] == 'w')ans += 1LL*(c - cntc[cur])*(cntw[cur] - 1);
}


int main(){
    INIT;
    cin >> n >> s;
    REP(i, n){
        if(s[i] == 'c')c++;
        else w++;
    }
    REP(i, n - 1){
        int a, b;
        cin >> a >> b;
        a--, b--;
        g[a].emplace_back(b);
        g[b].emplace_back(a);
    }
    dfs(0, -1);
    cout << ans << endl;
}