/*
* Author: Nonoze
* Created: Tuesday 24/12/2024
*/
#include <bits/stdc++.h>
using namespace std;
#ifndef _IN_LOCAL
#define dbg(...)
#endif
#define endl '\n'
#define endlfl '\n' << flush
#define quit(x) return (void)(cout << x << endl)
template<typename T> void read(T& x) { cin >> x;}
template<typename T1, typename T2> void read(pair<T1, T2>& p) { read(p.first), read(p.second);}
template<typename T> void read(vector<T>& v) { for (auto& x : v) read(x); }
template<typename T1, typename T2> void read(T1& x, T2& y) { read(x), read(y); }
template<typename T1, typename T2, typename T3> void read(T1& x, T2& y, T3& z) { read(x), read(y), read(z); }
template<typename T1, typename T2, typename T3, typename T4> void read(T1& x, T2& y, T3& z, T4& zz) { read(x), read(y), read(z), read(zz); }
template<typename T> void print(vector<T>& v) { for (auto& x : v) cout << x << ' '; cout << endl; }
#define sz(x) (int)(x.size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define make_unique(v) sort(all(v)), v.erase(unique(all(v)), (v).end())
#define pb push_back
#define mp(a, b) make_pair(a, b)
#define fi first
#define se second
#define cmin(a, b) a = min(a, b)
#define cmax(a, b) a = max(a, b)
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define QYES quit("YES")
#define QNO quit("NO")
#define int long long
#define double long double
const int inf = numeric_limits<int>::max() / 4;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1e9+7, LOG=20;
void solve();
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
int tt=1;
// cin >> tt;
while(tt--) solve();
return 0;
}
int A=27, B=1e9+7;
int fastpow(int x, int y) {
if (!y) return 1;
int z = fastpow(x, y/2); z = z*z % MOD;
if (y&1) z = z*x % MOD;
return z;
}
int n, k, m, q;
vector<int> a;
vector<vector<int>> adj;
vector<int> sz, centroid;
map<int, bool> cnt;
int ans=0;
void dfs(int u, int p=-1) {
sz[u]=1;
for (auto v: adj[u]) if (v!=p && !centroid[v]) {
dfs(v, u);
sz[u]+=sz[v];
}
}
int get_centroid(int u, int p, int tot) {
for (auto v: adj[u]) if (v!=p && !centroid[v] && sz[v]*2>tot) return get_centroid(v, u, tot);
return u;
}
void fill(int u, int p, int d, int hash, bool filling) {
if (filling) {
cnt[hash]=1;
} else if (cnt.count(hash)) {
cmax(ans, d*2-1);
}
for (auto v: adj[u]) if (v!=p && !centroid[v]) fill(v, u, d+1, (hash+fastpow(A, d)*a[v])%MOD, filling);
}
void fill2(int u, int p, int d, int hash, bool filling) {
if (filling) {
cnt[hash]=1;
} else if (cnt.count(hash)) {
cmax(ans, d*2);
}
for (auto v: adj[u]) if (v!=p && !centroid[v]) fill2(v, u, d+1, (hash+fastpow(A, d)*a[v])%MOD, filling);
}
void decompo(int u, int p=-1) {
dfs(u);
int c=get_centroid(u, -1, sz[u]); centroid[c]=1;
cnt.clear();
int hash=a[c];
for (auto v: adj[c]) if (!centroid[v]) {
int add=A*a[v];
fill(v, c, 2, hash+add, 0);
fill(v, c, 2, hash+add, 1);
}
cnt.clear();
cnt[hash]=1;
for (auto v: adj[c]) if (!centroid[v]) {
fill2(v, c, 1, a[v], 0);
fill2(v, c, 2, hash+a[v]*A, 1);
}
for (auto v: adj[c]) if (!centroid[v]) decompo(v, c);
}
void solve() {
read(n);
a.clear(), a.resize(n); for (auto& u: a) {
char x; cin >> x;
u=x-'0';
}
adj.clear(), adj.resize(n);
for (int i=1; i<n; i++) {
int u, v; read(u, v); u--, v--;
adj[u].pb(v), adj[v].pb(u);
}
sz.clear(), sz.resize(n), centroid.clear(), centroid.resize(n); decompo(0);
cout << ans << endl;
}
