#include<iostream>
#include<stack>
#include<map>
#include<vector>
#include<string>
#include<cassert>
#include<unordered_map>
#include <queue>
#include <cstdint>
#include<cstring>
#include<limits.h>
#include<cmath>
#include<set>
#include<algorithm>
#include <iomanip>
#include<numeric>
#include<complex>
#include<bitset>
using namespace std;
#define ll long long
#define f first
#define s second
#define pii pair<int,int>
#define ppii pair<int,pii>
#define vi vector<int>
#define pb push_back
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define F(n) for(int i=0;i<n;i++)
#define lb lower_bound
#define ub upper_bound
#define fastio ios::sync_with_stdio(false);cin.tie(NULL);
#pragma GCC optimize ("03,unroll-lopps")
#define int long long
#define double long double
using namespace std;
using cd = complex<double>;
double const PI=acos(-1);
const int mod=1e9+7,mxn=1e5+5,inf=1e18,minf=-1e18,lg=15,base=193;
//#undef int
int k,m,n,q,d;
void setIO(string name){
ios_base::sync_with_stdio(0); cin.tie(0);
freopen((name+".in").c_str(),"r",stdin);
freopen((name+".out").c_str(),"w",stdout);
}
vector<int>adj[mxn+10];
string a;
int del[mxn+10],sz[mxn+10];
int P[mxn+10],pinv[mxn+10],target;
int inv(int x){
int ex=mod-2,ans=1;
while(ex){
if(ex&1)ans=(ans*x)%mod;
x=(x*x)%mod;
ex>>=1;
}
return ans;
}
void getsz(int cur,int p){sz[cur]=1;for(auto i:adj[cur])if(i!=p&&!del[i])getsz(i,cur),sz[cur]+=sz[i];}
int getcen(int cur,int p,int need){
for(auto i:adj[cur])if(i!=p&&!del[i]){
if(sz[i]>(need/2))return getcen(i,cur,need);
}
return cur;
}
map<int,int>mp,lf;
vector<int>upd,upd2;
int node;
int up[mxn+10],val[mxn+10],val2[mxn+10],yes[mxn+10];
int dept[mxn+10],who[mxn+10];
bool dfs(int cur,int p){
if(dept[cur]>target)return 0;
up[cur]=p;
who[dept[cur]]=cur;
val[cur]=(val[p]+(a[cur-1]*P[dept[cur]])%mod)%mod;
val2[cur]=((val2[p]*base)%mod+a[cur-1])%mod;
int Y=who[dept[cur]-(dept[cur]+1)/2];
int g=((val[cur]-val[Y]+mod)%mod*pinv[dept[cur]-(dept[cur]+1)/2+1])%mod;
if(dept[cur]%2==0)Y=up[Y];
yes[cur]=(g==val2[Y]);
if(yes[cur]&&dept[cur]+1>=target)return 1;
int need=target-dept[cur]-1;
if(dept[cur]+1>=need){
int X=0;
if(dept[cur]-need<0)X=0;
else X=who[dept[cur]-need];
if(yes[X]){
g=((val[cur]-val[X]+mod)%mod*pinv[target-2*need])%mod;
if(mp[g])return 1;
upd2.pb(g);
}
}
if(dept[cur]<=(target/2)+1){
g=((val[cur]-a[node-1]+mod)%mod*pinv[1])%mod;
if(lf[g])return 1;
upd.pb(g);
}
for(auto i:adj[cur])if(i!=p&&!del[i]){
dept[i]=dept[cur]+1;
if(dfs(i,cur))return 1;
}
return 0;
}
bool solve(int cur){
getsz(cur,-1);
node=getcen(cur,-1,sz[cur]);
up[node]=dept[node]=0;
val[node]=val2[node]=a[node-1];
yes[node]=1;
who[0]=node;
for(auto i:adj[node]){
if(del[i])continue;
dept[i]=1;
if(dfs(i,node)){
upd.clear();
upd2.clear();
mp.clear();
lf.clear();
return 1;
}
for(auto j:upd)mp[j]=1;
for(auto j:upd2)lf[j]=1;
upd.clear();
upd2.clear();
}
lf.clear();
mp.clear();
del[node]=1;
for(auto i:adj[node])if(!del[i]){
if(solve(i))return 1;
}
return 0;
}
void re(){
for(int i=1;i<=n;i++)del[i]=0;
}
int32_t main(){
fastio
yes[0]=1;
cin>>n>>a;
P[0]=pinv[0]=1;
int div=inv(base);
for(int i=1;i<=n;i++)P[i]=(P[i-1]*base)%mod,pinv[i]=(pinv[i-1]*div)%mod;
for(int i=0;i<n-1;i++){
int u,v;cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
int ans=minf;
for(int k=0;k<2;k++){
int l=1,r=(n+1)/2;
while(l<=r){
int mid=l+(r-l)/2;
target=mid*2-k;
if(solve(1)){
l=mid+1,ans=max(ans,target);
}
else r=mid-1;
re();
}
}
ans=max(ans,1LL);
cout<<ans;
}
/*
*/
