#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
ll ctc[100000], ctw[100000];
bool used[100000];
vector<int> g[100000];
int n;
string s;
void dfs(int x){
	used[x]=1;
	if(s[x]=='c') ctc[x]++;
	else ctw[x]++;
	for(auto y:g[x]){
		if(used[y]) continue;
		dfs(y);
		ctc[x]+=ctc[y];
		ctw[x]+=ctw[y];
	}
}
ll ans;
void dfs2(int x){
	used[x]=1;
	ll sw=ctw[0]-1;
	for(auto y:g[x]){
		if(used[y]) continue;
		if(s[x]=='w'){
			ans+=((sw-ctw[y])*ctc[y]);
		}
		dfs2(y);
	}
	if(s[x]=='w') ans+=((ctc[0]-ctc[x])*(ctw[x]-1));
}

int main()
{
	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);
	}
	dfs(0);
	fill(used, used+n, 0);
	dfs2(0);
	cout<<ans<<endl;
	return 0;
}