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

int N;
ll ans;
ll C[100000];
ll W[100000];
vector<int> G[100000];
string S;

void dfs1(int n, int p) {
	if(S[n] == 'c') C[n]++;
	else W[n]++;
	for(auto c : G[n]) {
		if(c == p) continue;
		dfs1(c, n);
		C[n] += C[c];
		W[n] += W[c];
	}
}

void dfs2(int n, int p) {
	if(S[n] == 'w') {
		ll csum = C[0], wsum = W[0];
		for(auto c : G[n]) {
			ll cn = 0, wn = 0;
			if(c == p) {
				cn = csum - C[n];
				wn = wsum - W[n];
			}
			else {
				cn = C[c];
				wn = W[c];
			}
			ans += cn * (wsum - 1 - wn);
			//ans += wn * (csum - cn);
		}
	}
	for(auto c : G[n]) {
		if(c == p) continue;
		dfs2(c, n);
	}
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin >> N;
	cin >> S;
	for(int i = 0; i < N - 1; i++) {
		int a, b;
		cin >> a >> b;
		a--, b--;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	dfs1(0, -1);
	dfs2(0, -1);

	cout << ans << endl;
}