#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
#define name "main"
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define FORD(i,a,b) for(int i=(b);i>=(a);--i)
#define N 50000
const int MOD=998244353;
const int base=31;
vector<int>ke[N+2];
char s[N+2];
int power[N+2],h[N+2],up[N+2],val[N+2];
int n;
void add_edge(int u,int v){
ke[u].push_back(v),ke[v].push_back(u);
return;
}
int sub[N+2],dep[N+2],maxh=0;
map<int,bool> cnt[N+2];
bool del[N+2];
void dfs_size(int u,int p){
sub[u]=1;
for(auto&v:ke[u]){
if (v==p||del[v]) continue;
dfs_size(v,u);
sub[u]+=sub[v];
}
return;
}
int find_centroid(int u,int p,int half){
for(auto&v:ke[u]){
if (del[v]||v==p) continue;
if (sub[v]>half) return find_centroid(v,u,half);
}
return u;
}
bool calc(int root,int u,int p,int len){
dep[u]=dep[p]+1;
maxh=max(maxh,dep[u]);
if (dep[u]>len) return false;
h[dep[u]]=((LL)h[dep[u]-1]*base+val[u])%MOD;
up[dep[u]]=((LL)val[u]*power[dep[u]-1]+up[dep[u]-1])%MOD;
int need=((LL)up[dep[u]]*power[len-dep[u]]-h[dep[u]]+MOD)%MOD;
if (h[dep[u]]==up[dep[u]]&&dep[u]==len) {
return true;
}
if (cnt[len-dep[u]].find(need)!=cnt[len-dep[u]].end()) {
return true;
}
for(auto&v:ke[u]){
if (del[v]||v==p) continue;
if (calc(root,v,u,len)) return true;
}
return false;
}
void add(int u,int p,int len){
dep[u]=dep[p]+1;
maxh=max(maxh,dep[u]);
if (dep[u]>len) return;
h[dep[u]]=((LL)h[dep[u]-1]*base+val[u])%MOD;
up[dep[u]]=((LL)val[u]*power[dep[u]-1]+up[dep[u]-1])%MOD;
int need=((LL)up[dep[u]]*power[len-dep[u]]-h[dep[u]]+MOD)%MOD;
cnt[dep[u]][need]=true;
for(auto&v:ke[u]){
if (del[v]||v==p) continue;
add(v,u,len);
}
}
bool build(int u,int len){
dfs_size(u,u);
u=find_centroid(u,u,sub[u]/2);
del[u]=true;
maxh=0;
for(auto&v:ke[u]){
if (del[v]) continue;
h[1]=up[1]=val[u]; dep[u]=1;
if (calc(u,v,u,len)) return true;
dep[u]=0; h[0]=up[0]=0;
add(v,u,len);
}
FOR(i,0,maxh) cnt[i].clear();
for(auto&v:ke[u]) {
if (!del[v]) if (build(v,len)) return true;
}
return false;
}
bool check(int len){
if (len>n) return false;
if (len<=1) return true;
FOR(i,1,n) del[i]=false;
if (build(1,len)) return true;
return false;
}
int Getans(int l,int r,int p){
while(l<=r){
int m=(l+r)>>1;
if (check(2*m+p)) l=m+1; else r=m-1;
}
return (l-1)*2+p;
}
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin>>n;
FOR(i,1,n) {
char c; cin>>c;
val[i]=c-'a'+1;
}
FOR(i,1,n-1){
int u,v; cin>>u>>v;
add_edge(u,v);
}
power[0]=1;
FOR(i,1,n) power[i]=((LL)power[i-1]*base)%MOD;
cout<<max(Getans(0,n,0),Getans(0,n,1));
}
