#define _CRT_SECURE_NO_WARNINGS
#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<random>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())



int n;
string s;
int c[100000], w[100000];
vector<int> edge[100000];
int sw;
long long ans;


void dfs1(int par,int u) {
	c[u] = w[u] = 0;
	if (s[u] == 'c')c[u]++;
	else w[u]++;
	for (int v:edge[u]) {
		if (v == par)continue;
		dfs1(u, v);
		c[u] += c[v];
		w[u] += w[v];
	}
}

void dfs2(int par, int u,int pc,int pw){
	int ew = sw;
	if (s[u] == 'w')ew--;
	for (int v : edge[u]) {
		if (v == par)continue;
		if (s[u] == 'w')ans += (long long)(c[v])*(ew - w[v]);
		dfs2(u, v, pc + c[u] - c[v], pw + w[u] - w[v]);
	}
	if (s[u] == 'w')ans += (long long)(pc)*(ew - pw);
}




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

	cin >> n >> s;
	rep(i,n-1) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		edge[a].push_back(b);
		edge[b].push_back(a);
	}
	dfs1(-1, 0);
	sw = count(all(s), 'w');
	dfs2(-1, 0, 0, 0);
	cout << ans << endl;

	return 0;
}