#include <bits/stdc++.h>

#define F first
#define S second
#define all(x) x.begin(), x.end()
#define pb push_back
#define FIO ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0)

using namespace std;

typedef long long ll;
typedef pair <ll, ll> pii;

const int N = 3e5 + 7;

int n;
string s;
vector <int> adj[N];
ll dp[N][3][4];

void smax(ll &x, ll y) {x = max(x, y);}
void dfs(int x, int p = -1) {
	for (auto y : adj[x]) if (y != p) dfs(y, x);
	vector <ll> v;
	ll sum = 0;
	for (auto y : adj[x]) {
		if (y == p) continue;
		for (int o = 0; o < 2; o++) for (int i = 0; i < 4; i++) for (int j = 0; j < 3; j++) smax(dp[x][2*o][i], dp[y][j][2*o]);
		v.pb(dp[y][0][1]-dp[y][1][1]);
		sum += dp[y][1][1];
	}
	sort(all(v)); reverse(all(v));
	ll mx[3] = {sum, sum, sum};
	if (s[1] != s[2]) {
		for (int i = 0; i < v.size(); i++) {
			sum += v[i];
			for (int j = 0; j < 2; j++) smax(mx[j], (s[0] == s[2]) ? sum+(ll)(i+1)*(i+2*j) : sum+(ll)((i+1)/2+j)*((i+2)/2));
		}
		for (int i = 0; i < 4; i++) dp[x][1][i] = mx[i%2==0];
	}
	else {
		for (int i = 0; i < v.size(); i++) {
			sum += v[i];
			for (int j = 0; j < 3; j++) smax(mx[j], sum+(ll)(i+1+(!j))*(v.size()-i-1+(j==1)));
		}
		dp[x][1][0] = mx[0];
		dp[x][1][1] = dp[x][1][2] = mx[1];
		dp[x][1][3] = mx[2];
		for (int i = 0; i < 4; i++) smax(dp[x][2][i], dp[x][1][i]);
	}
}

int main () {
	FIO;
	cin >> n >> s;
	for (int i = 0; i < n-1; i++) {
		int x, y; cin >> x >> y; x--; y--;
		adj[x].pb(y);
		adj[y].pb(x);
	}
	if (s.size() == 1) {
		cout << n;
		return 0;
	}
	if (s.size() == 2) {
		cout << (n-1)*(1+(s[0]==s[1]));
		return 0;
	}
	if (s[0] == s[1] && s[1] == s[2]) {
		ll res = 0;
		for (int i = 0; i < n; i++) res += (ll)adj[i].size()*((ll)adj[i].size()-1);
		cout << res;
		return 0;
	}
	if (s[0] == s[1]) swap(s[0], s[2]);
	
	dfs(0);
	cout << max(dp[0][0][3], max(dp[0][1][3], dp[0][2][3]));

	return 0;
}