#include<bits/stdc++.h>
#define fi first
#define se second
#define int long long
using namespace std;
using ll = long long;
using ii = pair<int, int>;
using aa = array<int,4>;
const int N = 1e5+5;
const ll INF = 1e18;
const int MOD = 1e9+7;
const int base = 31;
int n, u, v, root, mid, mx = 0, ans ;
bool ok;
//hashing
int po[N], a[N];
//centroid
int sz[N];
bool num[N];
vector <aa> anc[N];
// tree
char c;
vector <int> adj[N];
//answer
map<int,bool> mp[N];
void getSize(int u,int p){
sz[u] = 1;
for (int it : adj[u]){
if (it == p || num[it]) continue;
getSize(it,u);
sz[u] += sz[it];
}
}
int getCentroid(int u,int p,int n){
for (int it : adj[u]){
if (it == p || num[it]) continue;
if (sz[it] * 2 > n) return getCentroid(it,u,n);
}
return u;
}
void dfs(int u,int p,int cur,int depth,int type){
if (depth > (mid + 1) / 2) return;
if (!type){
if (mp[mid / 2][cur] == 1){
ok = 1;
}
} else{
mx = max(mx,depth);
mp[depth][cur] = 1;
}
if (ok) return;
for (int it : adj[u]){
if (it == p || num[it]) continue;
if (mid & 1) dfs(it,u,(cur * po[depth + 1] + a[it]) % MOD,depth + 1,type);
else{
if (type) dfs(it,u,(cur * po[depth + 1] + a[it]) % MOD,depth + 1,1);
else dfs(it,u,(cur * po[depth + 2] + a[it]) % MOD,depth + 1,0);
}
}
}
void decompose(int u){
getSize(u,0);
int m = sz[u];
root = getCentroid(u,0,m);
num[root] = 1;
mx = 0;
mp[0][0] = 1;
for (int it : adj[root]){
if (num[it]) continue;
if (mid % 2 == 0){
// mid chan
dfs(it,root,a[root] * po[2] + a[it],1,0);
} else{
dfs(it,root,a[it],1,0);
}
dfs(it,root,a[it],1,1);
}
//cout << root << '\n';
for (int i = 1; i <= mx; i++){
mp[i].clear();
}
if (ok) return;
for (int it : adj[root]){
if (num[it]) continue;
decompose(it);
}
}
bool check(){
ok = 0;
for (int i = 1; i <= n; i++) num[i] = 0;
decompose(1);
return ok;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);cout.tie(NULL);
cin >> n;
for (int i = 1; i <= n; i++){
cin >> c;
a[i] = (c - 'a' + 1);
}
ans = 1;
for (int i = 1; i < n; i++){
cin >> u >> v;
adj[u].push_back(v);
adj[v].push_back(u);
if (a[u] == a[v]) ans = 2;
}
po[0] = 1;
for (int i = 1; i <= n; i++){
po[i] = po[i-1] * base % MOD;
}
int l = 1, r = n / 2;
while (l <= r){
mid = (l + r) >> 1;
mid *= 2;
if (check()){
ans = max(ans,mid);
l = mid / 2 + 1;
} else r = mid / 2 - 1;
}
l = 1, r = n / 2;
while (l <= r){
mid = (l + r) >> 1;
mid = mid * 2 - 1;
if (check()){
ans = max(ans,mid);
l = (mid + 1) / 2 + 1;
} else r = (mid + 1) / 2 - 1;
}
cout << ans;
return 0;
}
