#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <array>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cmath>
#include <ctime>
#include <iomanip>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <random>
#include <utility>
#include <functional>
using namespace std;
void solve()
{
	int N;
	string S;
	cin >> N >> S;
	vector<vector<int>> G(N);
	for(int i = 1;i < N;i++)
	{
		int u,v;
		cin >> u >> v;
		u--; v--;
		G[u].push_back(v);
		G[v].push_back(u);
	}
	vector<int> C(N),W(N);
	auto dfs = [&](auto dfs,int u,int p) -> void
	{
		if(S[u] == 'c') C[u]++;
		else W[u]++;
		for(int v : G[u]) if(v != p)
		{
			dfs(dfs,v,u);
			C[u] += C[v];
			W[u] += W[v];
		}
	};
	dfs(dfs,0,-1);
	long long ans = 0;
	for(int u = 0;u < N;u++) if(S[u] == 'w')
	{
		long long cur = (long long)C[0] * (W[0] - 1);
		for(int v : G[u])
		{
			int c = 0,w = 0;
			if(C[v] > C[u] || W[v] > W[u])
			{
				c = C[0] - C[u];
				w = W[0] - W[u];
			}
			else
			{
				c = C[v];
				w = W[v];
			}
			cur -= (long long)c * w;
		}
		ans += cur;
	}
	cout << ans << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) solve();
}