#include<bits/stdc++.h>
using namespace std;
#define int long long
const int maxn=5e4+7;
const int mod=1e9+7;
const int base=9973;
int lo[maxn];
vector<int>adj[maxn];
int subsz[maxn];
bool removed[maxn];
int dis[maxn];
int color[maxn];
int curdn[maxn];
int down[maxn];
bool pal[maxn];
int up[maxn];
bool bb=0;
vector<int>toadd_l,toadd_s;
set<int>hashl,hashs;
string s;
int n;
int curlen;
int get(int l,int r,int x,int y){
return (y-(lo[(r-l)]*x)%mod+2*mod)%mod;
}
int get_subsize(int u,int par){
subsz[u]=1;
for(int v:adj[u]){
if(removed[v]||v==par)continue;
get_subsize(v,u);
subsz[u]+=subsz[v];
}
return subsz[u];
}
int find_cen(int u,int par,int treesize){
for(int v:adj[u]){
if(removed[v]||v==par)continue;
if((subsz[v]*2)>treesize)return find_cen(v,u,treesize);
}
return u;
}
void dfs(int u,int par){
if(bb)return;
dis[u]=dis[par]+1;
if(dis[u]>curlen)return;
curdn[dis[u]]=u;
down[u]=(down[par]*base%mod+color[u])%mod;
up[u]=(up[par]+color[u]*lo[dis[u]]%mod)%mod;
pal[u]=(down[u]==up[u]);
if(dis[u]==curlen){
bb=pal[u];
}
else if(dis[u]>curlen/2){
int diff=dis[u]*2-curlen;
int c=curdn[diff];
if(pal[c]){
int hn=get(dis[c]-1,dis[u],down[curdn[diff-1]],down[u]);
if(hashs.count(hn))bb=1;
toadd_l.push_back(hn);
}
}
else{
if(hashl.count(down[u]))bb=1;
toadd_s.push_back(down[u]);
}
if(dis[u]*2==curlen){
if(hashs.count(down[u]))bb=1;
}
for(int v:adj[u]){
if(v==par||removed[u])continue;
dfs(v,u);
}
}
void centroid_decomp(int u=1){
if(bb)return;
int cen=find_cen(u,0,get_subsize(u,0));
removed[cen]=1;
curdn[0]=cen;
dis[cen]=0;
down[cen]=color[cen];
up[cen]=color[cen];
for(int v:adj[cen]){
if(removed[v])continue;
dfs(v,cen);
for(int x:toadd_l)hashl.insert(x);
for(int x:toadd_s)hashs.insert(x);
toadd_l.clear();
toadd_s.clear();
}
hashl.clear();
hashs.clear();
for(int v:adj[cen]){
if(removed[v]==0){
centroid_decomp(v);
}
}
}
bool check(int length){
if(length==1)return true;
curlen=length-1;
for(int i=1;i<=n;i++)removed[i]=0;
bb=0;
centroid_decomp();
return bb;
}
main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>n;
lo[0]=1;
for(int i=1;i<=n;i++)lo[i]=(lo[i-1]*base)%mod;
cin>>s;
s=" "+s;
for(int i=1;i<=n;i++)color[i]=s[i]-'a'+1;
for(int i=1;i<n;i++){
int x,y;
cin>>x>>y;
adj[x].push_back(y);
adj[y].push_back(x);
}
//odd len
int l=0,r=n/2-((n%2)==0);
int res=0;
while(l<=r){
int m=(l+r)/2;
if(check(2*m+1)){
res=max(res,2*m+1);
l=m+1;
}
else r=m-1;
}
l=(res)/2+1,r=n/2;
while(l<=r){
int m=(l+r)/2;
if(check(2*m)){
res=max(res,2*m);
l=m+1;
}
else r=m-1;
}
cout<<res;
}
