#include<bits/stdc++.h>
#define int long long
#define ii pair<int,int>
#define fi first
#define se second
using namespace std;
const int N = 5e4 + 5, base = 311, mod = 1e9 + 7;
int n, sz[N], h[N], ans;
int up[N], down[N], H, mx_h;
int Pow[N], a[N];
bool is_centroid[N];
string s;
vector<int> g[N];
map<int, bool> d[N];
void dfs(int u, int par = -1){
sz[u] = 1;
for(int v : g[u]){
if(v == par || is_centroid[v]) continue;
dfs(v, u);
sz[u] += sz[v];
}
}
int find_centroid(int u, int tree_sz, int par = -1){
for(int v : g[u]){
if(v != par && !is_centroid[v] && sz[v] > tree_sz/2)
return find_centroid(v, tree_sz, u);
}
return u;
}
bool get(int u, int par = 0){
h[u] = h[par] + 1;
mx_h = max(mx_h, h[u]);
if(h[u] > H) return 0;
down[h[u]] = (down[h[u] - 1]*base + a[u]) % mod;
up[h[u]] = (s[u] * Pow[h[u] - 1] + up[h[u] - 1]) % mod;
int tmp = (up[h[u]] * Pow[H - h[u]] - down[h[u]] + mod) % mod;
if(up[h[u]] == down[h[u]] && h[u] == H) return 1;
if(d[H - h[u]][tmp]) return 1;
for(int v : g[u]){
if(v != par && !is_centroid[v])
if(get(v, u)) return 1;
}
return 0;
}
void update(int u, int par = 0){
h[u] = h[par] + 1;
mx_h = max(mx_h, h[u]);
if(h[u] > H) return;
down[h[u]] = (down[h[u] - 1]*base + a[u]) % mod;
up[h[u]] = (s[u] * Pow[h[u] - 1] + up[h[u] - 1]) % mod;
int tmp = (up[h[u]] * Pow[H - h[u]] - down[h[u]] + mod) % mod;
d[h[u]][tmp] = 1;
for(int v : g[u])
if(v != par && !is_centroid[v])
update(v, u);
}
bool build_centroid(int u){
dfs(u);
int centroid = find_centroid(u, sz[u]);
is_centroid[u] = 1;
for(int v : g[centroid]){
if(!is_centroid[v]){
h[centroid] = 1;
up[1] = down[1] = a[centroid];
if(get(v, centroid)) return 1;
h[centroid] = up[0] = down[0] = 0;
update(v);
}
}
for(int i = 0; i < mx_h; i++)
d[i].clear();
for(int v : g[centroid])
if(!is_centroid[v] && build_centroid(v))
return 1;
return 0;
}
bool check(int x){
for(int i = 1; i <= n; i++){
d[i].clear();
is_centroid[i] = 0;
}
H = x;
return build_centroid(1);
}
void solve(){
int l = 1, r = n/2;
while(l <= r){
int mid = l + r >> 1;
if(check(mid << 1)){
l = mid + 1;
ans = mid << 1;
} else {
r = mid - 1;
}
}
l = 1, r = n/2 + 1;
while(l <= r){
int mid = l + r >> 1;
if(check(mid << 1 | 1)){
l = mid + 1;
ans = max(ans, mid << 1 | 1);
} else {
r = mid - 1;
}
}
cout << ans;
}
main(){
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> s;
s = ' ' + s;
for(int i = 1; i <= n; i++)
a[i] = s[i] - 'a' + 1;
// for(int i = 1; i <= n; i++)
// cout << a[i] << ' ';
for(int i = 1; i < n; i++){
int u, v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
Pow[0] = 1;
for(int i = 1; i <= n; i++){
Pow[i] = (Pow[i - 1] * base) % mod;
}
solve();
}
