#include <bits/stdc++.h>
using namespace std;
const int N = 50007;
const unsigned long long base = 311;
int n, sub[N], dep[N];
bool del[N];
char a[N];
vector<int> adj[N];
unsigned long long pw[N], up[N], dw[N];
map<unsigned long long, bool> mp[N];
void dfs (int u, int p = 0){
sub[u] = 1;
for (int v : adj[u]){
if (v != p && !del[v]){
dfs(v, u);
sub[u] += sub[v];
}
}
return;
}
int findCentroid (int u, int sz, int p = 0){
for (int v : adj[u]){
if (v != p && !del[v] && sub[v] * 2 > sz){
return findCentroid(v, sz, u);
}
}
return u;
}
void dfsHash (int u, int p = 0, int d = 1){
if (p != 0){
dw[u] = dw[p] * base + 1ull * (int)(a[u]);
}
up[u] = up[p] + 1ull * (int)(a[u]) * pw[d - 1];
dep[u] = d;
for (int v : adj[u]){
if (v != p && !del[v]){
dfsHash(v, u, d + 1);
}
}
return;
}
bool dfsSolve (int u, int p, int len){
if (dep[u] > len){
return false;
}
unsigned long long f = up[u] * pw[len - dep[u]] - dw[u];
if (mp[len - dep[u] + 1].count(f)){
return true;
}
for (int v : adj[u]){
if (v != p && !del[v]){
if (dfsSolve(v, u, len)){
return true;
}
}
}
return false;
}
int mx;
void dfsAdd (int u, int p, int len){
if (dep[u] > len){
return;
}
unsigned long long f = up[u] * pw[len - dep[u]] - dw[u];
mp[dep[u]][f] = true;
mx = max(mx, dep[u]);
for (int v : adj[u]){
if (v != p && !del[v]){
dfsAdd(v, u, len);
}
}
return;
}
bool centroid (int u, int len){
dfs(u);
u = findCentroid(u, sub[u]);
dfsHash(u);
mx = 0;
mp[1][up[u] * pw[len - dep[u]] - dw[u]] = true;
for (int v : adj[u]){
if (!del[v]){
if (dfsSolve(v, u, len)){
return true;
}
dfsAdd(v, u, len);
}
}
for (int i = 1; i <= mx; ++i){
mp[i].clear();
}
del[u] = true;
for (int v : adj[u]){
if (!del[v]){
if (centroid(v, len)){
return true;
}
}
}
return false;
}
int32_t main (){
ios::sync_with_stdio(false); cin.tie(nullptr);
const string task = "test";
if (fopen ((task + ".inp").c_str(), "r")){
freopen ((task + ".inp").c_str(), "r", stdin);
freopen ((task + ".out").c_str(), "w", stdout);
}
pw[0] = 1ull;
for (int i = 1; i < N; ++i){
pw[i] = pw[i - 1] * base;
}
cin >> n;
for (int i = 1; i <= n; ++i){
cin >> a[i];
}
for (int i = 1; i < n; ++i){
int u, v; cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
}
int l = 1, r = (n >> 1), ans = 1;
while (l <= r){
int m = l + r >> 1;
for (int i = 1; i <= n; ++i){
del[i] = false;
}
if (centroid(1, m * 2)){
ans = max(ans, m * 2);
l = m + 1;
} else {
r = m - 1;
}
}
l = 1; r = ((n - 1) >> 1);
while (l <= r){
int m = l + r >> 1;
for (int i = 1; i <= n; ++i){
del[i] = false;
}
if (centroid(1, m * 2 + 1)){
ans = max(ans, m * 2 + 1);
l = m + 1;
} else {
r = m - 1;
}
}
cout << ans << "\n";
}
