/*
* 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 inv(int x) { return fastpow(x, MOD-2); }
int n, k, m, q;
vector<int> a;
vector<vector<int>> adj;
vector<int> sz, centroid, child;
map<pair<int, int>, bool> cnt;
int obj;
bool works;
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 hashminus, int hashplus, bool filling, int cur) {
if (d>obj*2) return;
int hash=(hashplus-hashminus+MOD)%MOD;
if (d<obj) hash*=fastpow(A, obj-d);
if (filling) {
cnt[{d, hash}]=1;
} else if (cnt.count({obj*2-d, hash})) {
works=1;
}
// cout << hash << ' ' << d << ' ' << filling << endl;
// cout << hashminus << ' ' << hashplus << endl;
int newcur=cur;
if (d>=obj) newcur=child[cur];
for (auto v: adj[u]) if (v!=p && !centroid[v]) {
int newhashminus = (hashminus*A)%MOD;
int newhashplus = hashplus + fastpow(A, min(obj, d))*a[v];
if (d>=obj) {
newhashminus=(newhashminus+a[cur])%MOD;
newhashplus=((newhashplus-a[cur]+MOD)*inv(A))%MOD;
}
child[u]=v;
fill(v, u, d+1, newhashminus, newhashplus, filling, newcur);
}
}
void fill2(int u, int p, int d, int hashminus, int hashplus, bool filling, int cur) {
if (d>obj*2+1) return;
int hash=(hashplus-hashminus+MOD)%MOD;
if (d<obj) hash*=fastpow(A, obj-d);
if (filling) {
cnt[{d, hash}]=1;
} else if (cnt.count({obj*2+1-d, hash})) {
works=1;
}
// cout << hashminus << ' ' << hashplus << ' ' << hash << ' ' << d << ' ' << filling << ' ' << cur+1 << endl;
int newcur=cur;
if (d>=obj) newcur=child[cur];
for (auto v: adj[u]) if (v!=p && !centroid[v]) {
int newhashminus = (hashminus*A)%MOD;
int newhashplus = hashplus + fastpow(A, min(obj, d))*a[v];
if (d>=obj) {
if (d>obj) newhashminus=(newhashminus+a[cur])%MOD;
// cout << newhashplus << ' ' << a[child[cur]] << ' ' << child[cur] << endl;
newhashplus=(((newhashplus-a[child[cur]]+MOD)%MOD)*inv(A))%MOD;
}
child[u]=v;
fill2(v, u, d+1, newhashminus, newhashplus, filling, newcur);
}
}
void decompo(int u, bool pair, int p=-1) {
dfs(u);
int c=get_centroid(u, -1, sz[u]); centroid[c]=1;
cnt.clear(); cnt[{1, (a[c]*fastpow(A, obj-1))%MOD}]=1;
// cout << (a[c]*fastpow(A, obj-1))%MOD << endl;
for (auto v: adj[c]) if (!centroid[v]) {
if (pair) {
child[c]=v;
fill(v, c, 1, 0, a[v], 0, v);
fill(v, c, 2, 0, a[c]+A*a[v], 1, c);
} else {
child[n]=c, child[c]=v;
fill2(v, c, 1, 0, a[v], 0, c);
fill2(v, c, 2, 0, (obj>1?a[c]+A*a[v]:a[v]), 1, (obj>1?n:c));
}
// cout << endl;
}
// cout << "OK " << c+1 << endl;
for (auto v: adj[c]) if (!centroid[v]) decompo(v, pair, c);
}
void solve() {
read(n);
a.clear(), a.resize(n); for (auto& u: a) {
char x; cin >> x;
u=x-'a'+1;
}
adj.clear(), adj.resize(n), child.clear(), child.resize(n+1);
int l=2, r=n/2, ans=1;
for (int i=1; i<n; i++) {
int u, v; read(u, v); u--, v--;
adj[u].pb(v), adj[v].pb(u);
if (a[u]==a[v]) ans=2;
}
while (l<=r) {
int mid=(l+r)/2;
works=0, obj=mid, sz.clear(), sz.resize(n), centroid.clear(), centroid.resize(n);
decompo(0, 1);
if (works) ans=mid*2, l=mid+1;
else r=mid-1;
}
l=1, r=(n-(1-n%2))/2;
while (l<=r) {
int mid=(l+r)/2;
works=0, obj=mid, sz.clear(), sz.resize(n), centroid.clear(), centroid.resize(n);
decompo(0, 0);
if (works) cmax(ans, mid*2+1), l=mid+1;
else r=mid-1;
}
cout << ans << endl;
}
