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

using int64 = long long;

const int MAX_N = 100000;

vector<int> T[MAX_N];
int64 c[MAX_N], w[MAX_N];

int N;
string S;

int64 allc = 0, allw = 0;

int64 dfs(int v, int par) {
    if (S[v] == 'c') c[v]++;
    else w[v]++;

    int64 ans = 0, add = 0;
    int64 cumc = 0, cumw = 0;

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

        cumc += c[to]; cumw += w[to];
        add -= c[to] * w[to];
    }
    int64 upc = allc - c[v],
          upw = allw - w[v];
    cumc += upc; cumw += upw;
    add -= upc * upw;
    add += cumc * cumw;

    if (S[v] != 'w') add = 0;
    ans += add;

    return ans;
}

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

    for (char ch : S) {
        if (ch == 'c') allc++;
        else allw++;
    }

    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);
    }

    cout << dfs(0, -1) << endl;

    return 0;
}