#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ar array
const int mxN=5e4, M=1e9+696969;
const ar<int, 2> P={129, 9172};
int n, sz[mxN], ts, ans=1;
string s;
vector<int> adj[mxN];
bool dead[mxN];
ar<int, 2> pp[mxN];
map<ar<int, 2>, int> mp[mxN+1];
ar<int, 2> operator+(ar<int, 2> a, ar<int, 2> b) {
for (int i : {0, 1})
if ((a[i]+=b[i])>=M)
a[i]-=M;
return a;
}
ar<int, 2> operator-(ar<int, 2> a, ar<int, 2> b) {
for (int i : {0, 1})
if ((a[i]-=b[i])<0)
a[i]+=M;
return a;
}
ar<int, 2> operator*(ar<int, 2> a, ar<int, 2> b) {
for (int i : {0, 1})
a[i]=(ll)a[i]*b[i]%M;
return a;
}
struct Hash {
ar<int, 2> a={}, b={};
int length=0;
};
vector<vector<Hash>> cmps;
Hash operator+(Hash a, Hash b) {
return {a.a*pp[b.length]+b.a, b.b*pp[a.length]+a.b, a.length+b.length};
}
Hash mk(char c) {
ar<int, 2> id={c, c};
return {id, id, 1};
}
int dfs1(int u, int p=-1) {
sz[u]=1;
for (int v : adj[u])
if (!dead[v]&&v!=p)
sz[u]+=dfs1(v, u);
return sz[u];
}
int dfs2(int u, int p=-1) {
for (int v : adj[u])
if (!dead[v]&&v!=p&&sz[v]>ts/2)
return dfs2(v, u);
return u;
}
void dfs3(int u, int p=-1, Hash h=Hash()) {
h=h+mk(s[u]);
cmps.back().push_back(h);
for (int v : adj[u])
if (!dead[v]&&v!=p)
dfs3(v, u, h);
}
bool ok(int rt, int x) {
for (int rep=0; rep<2; ++rep, ++x) {
for (vector<Hash>& v : cmps)
for (Hash& h : v)
if (h.length+2<=x)
++mp[h.length][h.b*pp[x-h.length]-h.a];
for (vector<Hash>& v : cmps) {
for (Hash& h : v)
if (h.length+2<=x)
--mp[h.length][h.b*pp[x-h.length]-h.a];
for (Hash h : v) {
if (h.length+1>=x)
continue;
swap(h.a, h.b);
h=h+mk(s[rt]);
ar<int, 2> cur=h.a*pp[x-h.length]-h.b;
auto it=mp[x-h.length].find(cur);
if (it!=mp[x-h.length].end()&&it->second) {
for (int i=1; i+2<=x; ++i)
mp[i].clear();
return 1;
}
}
for (Hash& h : v)
if (h.length+2<=x)
++mp[h.length][h.b*pp[x-h.length]-h.a];
}
for (int i=1; i+2<=x; ++i)
mp[i].clear();
}
return 0;
}
void dfs4(int u=0) {
ts=dfs1(u);
u=dfs2(u);
cmps.clear();
for (int v : adj[u])
if (!dead[v]) {
cmps.push_back({});
dfs3(v, u);
}
for (vector<Hash>& v : cmps)
for (Hash& h : v) {
Hash x=mk(s[u])+h;
if (x.a==x.b)
ans=max(ans, x.length);
}
if (ans>=ts)
return;
int lb=ans, rb=ts;
while(lb<rb) {
int mid=(lb+rb+1)/2;
if (ok(u, mid))
lb=mid;
else
rb=mid-1;
}
ans=max(ans, lb);
dead[u]=1;
for (int v : adj[u])
if (!dead[v])
dfs4(v);
}
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
pp[0]={1, 1};
for (int i=1; i<mxN; ++i)
pp[i]=pp[i-1]*P;
cin >> n >> s;
for (int i=1; i<n; ++i) {
int u, v;
cin >> u >> v, --u, --v;
adj[u].push_back(v);
adj[v].push_back(u);
}
dfs4();
cout << ans;
return 0;
}
