// #pragma GCC optimize("O3")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include <bits/stdc++.h>
using namespace std;

#define PB emplace_back
#define int long long
#define ll long long
#define vi vector<int>
#define siz(a) ((int) ((a).size()))
#define rep(i, a, b) for (int i = (a); i <= (b); ++i)
#define per(i, a, b) for (int i = (a); i >= (b); --i)
void print(vi n) { rep(i, 0, siz(n) - 1) cerr << n[i] << " \n"[i == siz(n) - 1]; }

const int N = 3e5;
int a, b[3], id, f[N + 5][3][3];
struct pii {
	int x, y, z;
	int &operator[](const int &o) {
		if(o == 0) return x;
		if(o == 1) return y;
		return z;
	}
} g[N + 5];
char c[4];
vi st[N + 5];

void dfs(int n, int fa) {
	if(fa) st[n].erase(find(st[n].begin(), st[n].end(), fa));
	for(int v : st[n]) dfs(v, n);
	rep(x, 0, id) {
		int siz = 0;
		for(int v : st[n]) {
			++siz;
			rep(i, 0, id) g[siz][i] = f[v][i][x];
			// g[siz][0] = f[v][0][x];
			// g[siz][1] = f[v][1][x];
			// g[siz][2] = f[v][2][x];
		}
		// cout << n << ' ' << siz << endl;
		rep(y, 0, id) {
			int p[3] = {0, 0, 0};
			if(fa) {
				p[b[0]] += x == b[1] && y == b[2];
				p[b[2]] += x == b[1] && y == b[0];
			}
			if(x != b[1]) {
				rep(i, 1, siz) f[n][x][y] += max({g[i][0] + p[0], g[i][1] + p[1], g[i][2] + p[2]});
				continue;
			}
			int now = 0;
			if(id == 2) {
				rep(i, 1, siz) assert(g[i][0] == g[i][2]);
				rep(i, 1, siz) now += g[i][0];
				sort(g + 1, g + siz + 1, [&] (pii x, pii y) {
					return x[1] - x[0] > y[1] - y[0];
				});
				rep(i, 0, siz) {
					int j = siz - i;
					rep(k, max(0ll, j / 2 - 2), min(j, j / 2 + 2)) // 0 : k, 1 : i, 2 : j - k
					f[n][x][y] = max(f[n][x][y],
					p[0] * k + p[1] * i + p[2] * (j - k)
					+ k * (j - k)
					+ now);
					if(i < siz) now += g[i + 1][1] - g[i + 1][0];
				}
			}
			else {
				// cout << p[0] << ' ' << p[1] << ' ' << x << ' ' << y << endl;
				// cout << "!@#!" << endl;
				assert(!b[2]);
				int now = 0;
				rep(i, 1, siz) now += g[i][1];
				sort(g + 1, g + siz + 1, [&] (pii x, pii y) {
					return x[0] - x[1] > y[0] - y[1];
				});
				// cout << n << ' ' << now << endl;
				rep(i, 0, siz) { // sum of 0
					int j = siz - i;
					f[n][x][y] = max(f[n][x][y],
					p[0] * i + p[1] * j
					+ ((b[0] == 0 && b[2] == 1) + (b[0] == 1 && b[2] == 0)) * i * j
					+ (b[0] == 0 && b[2] == 0) * i * (i - 1)
					+ (b[0] == 1 && b[2] == 1) * j * (j - 1)
					+ now);
					if(i < siz) now += g[i + 1][0] - g[i + 1][1];
				}
				// cout << now << endl;
			}
		}
	}
	if(n == 1) {
		// cout << f[4][0][1] << endl;
		cout << max({f[1][0][0], f[1][1][0], f[1][2][0]});
		exit(0);
	}
}

signed main() {
	// freopen(".in", "r", stdin);
	// freopen(".out", "w", stdout);
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	cin >> a >> c;
	// cout << strlen(c);
	if(strlen(c) == 1) return cout << a, 0;
	if(strlen(c) == 2) return cout << (c[0] == c[1] ? 2 * (a - 1) : a - 1), 0;
	rep(i, 1, 2) {
		b[i] = ++id;
		rep(j, 0, i - 1) if(c[i] == c[j]) {
			--id;
			b[i] = b[j];
		}
	}
	int x, y;
	rep(i, 1, a - 1) {
		cin >> x >> y;
		st[x].PB(y), st[y].PB(x);
	}
	dfs(1, 0);
	return cerr << endl << 1.0 * clock() / CLOCKS_PER_SEC << endl, 0;
}