#include <iostream>
#include <vector>
using namespace std;

using int64 = long long;

const int MAX_N = 100000;

vector<int> T[MAX_N];
int c[MAX_N], w[MAX_N], parent[MAX_N];

int N;
string S;

void dfs(int v, int par) {
    if (S[v] == 'c') c[v]++;
    else w[v]++;

    parent[v] = par;

    for (int to : T[v]) {
        if (to == par) continue;
        dfs(to, v);
        c[v] += c[to];
        w[v] += w[to];
    }
}

int main() {
    cin >> N >> S;

    for (int i = 0; i < N - 1; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        T[a].push_back(b);
        T[b].push_back(a);
    }

    dfs(0, -1);

    int64 ans = 0;
    for (int v = 0; v < N; v++) {
        if (S[v] != 'w') continue;
        int64 upc = c[0] - c[v],
              upw = w[0] - w[v];
        int64 cumc = upc,
              cumw = upw;
        ans -= upc * upw;

        for (int to : T[v]) {
            if (to == parent[v]) continue;
            cumc += c[to];
            cumw += w[to];
            ans -= c[to] * w[to];
        }
        ans += cumc * cumw;
    }
    cout << ans << endl;

    return 0;
}