#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
long long p1 = 104729,p2=7927,m=29,sz[50100],n,p[50100],cp[50100],ans;
pair<ll,ll> pow_v[50100],up_v[50100];
bool dead[50100],pel[50100];
set<pair<ll,pair<ll,ll> > >tot; //with_root
vector<ll> g[50100];
string s;
// -> t*m+v
// <- t+v*pow()
void get_sz(ll start,ll parent)
{
sz[start] = 1;
for(ll next:g[start])
{
if(dead[next] ||parent == next)
continue;
get_sz(next,start);
sz[start] += sz[next];
}
}
ll get_centroid(ll start,ll parent,ll tree_sz)
{
for(ll next:g[start])
{
if(dead[next]||next==parent)
continue;
if(sz[next]>tree_sz/2)
return get_centroid(next,start,tree_sz);
}
return start;
}
pair<ll,ll> left_push(pair<ll,ll> hash_v,ll v)
{
return {(hash_v.first*m+v)%p1,(hash_v.second*m+v)%p2};
}
pair<ll,ll> right_add(pair<ll,ll> hash_v,ll v,ll ind)
{
return {(hash_v.first+pow_v[ind].first*v)%p1,(hash_v.second+pow_v[ind].second*v)%p2};
}
void check_pel(ll start,ll parent,ll d,pair<ll,ll> up,pair<ll,ll> down)
{
up = left_push(up,(ll)(s[start]-'a'));
down = right_add(down,(ll)(s[start]-'a'),d);
up_v[start] = up;
if(up.first==down.first&&up.second==down.second)
pel[start] = true;
else
pel[start] = false;
for(ll next:g[start])
{
if(dead[next] || parent == next)
continue;
check_pel(next,start,d+1,up,down);
}
}
void update(ll start,ll parent,ll d)
{
pair<ll,ll> up = up_v[start];
for(ll next:g[start])
{
if(dead[next] || parent == next)
continue;
update(next,start,d+1);
}
pair<ll,pair<ll,ll> > hash_v = {d,up};
tot.insert(hash_v);
}
void cal_c(ll start,ll parent,ll l,ll d)
{
p[start] = parent;
if(d==l)
{
cp[start] = start;
return;
}
if(g[start].size()==1&&2*d-l>0)
{
cp[start] = start;
for(ll i=0;i<l-d;i++)
cp[start] = p[cp[start]];
return;
}
for(ll next:g[start])
{
if(dead[next] || parent==next)
continue;
cal_c(next,start,l,d+1);
cp[start] = cp[next];
}
if(2*d-l>0)
cp[start] = p[p[cp[start]]];
}
bool dfs_pel(ll start,ll parent,ll l,ll d) // l is length of pel, d is depth, l-d for other sub tree, 2d-l+1>=0, up is better for calculate
{
if(d>l)
return false;
for(ll next:g[start])
{
if(next==parent||dead[next])
continue;
if(dfs_pel(next,start,l,d+1))
return true;
}
if(2*d-l<=0||!pel[cp[start]])
return false;
if(2*d-l-1==0)
return tot.find({d,{up_v[start]}})!=tot.end();
pair<ll,ll> pel_s = up_v[p[cp[start]]];
pair<ll,ll> hash_v = {((up_v[start].first-pow_v[l-d+1].first*pel_s.first)%p1+p1)%p1,((up_v[start].second-pow_v[l-d+1].second*pel_s.second)%p2+p2)%p2};
return tot.find({l-d+1,hash_v})!=tot.end();
}
bool centroid_decomposition(ll start,ll l)
{
get_sz(start,-1);
ll c = get_centroid(start,-1,sz[start]);
dead[c]=true;
for(ll next:g[c])
{
if(!dead[next]&¢roid_decomposition(next,l))
{
dead[c] = false;
return true;
}
}
tot.clear();
pair<ll,ll> root = left_push({(ll)0,(ll)0},(ll)(s[c]-'a'));
tot.insert({1,root});
check_pel(c,-1,0,{(ll)0,(ll)0},{(ll)0,(ll)0});
cal_c(c,-1,l,1);
for(ll next:g[c])
{
if(dead[next])
continue;
if(dfs_pel(next,c,l,2))
{
dead[c] = false;
return true;
}
update(next,c,2);
}
tot.clear();
tot.insert({1,root});
for(ll i = g[c].size()-1;i>=0;i--)
{
ll next = g[c][i];
if(dead[next])
continue;
if(dfs_pel(next,c,l,2))
{
dead[c] = false;
return true;
}
update(next,c,2);
}
dead[c] = false;
return false;
}
void init(ll n)
{
pow_v[0] = {(ll) 1,(ll) 1};
for(ll i=1;i<n;i++)
pow_v[i] = {pow_v[i-1].first*m%p1,pow_v[i-1].second*m%p2};
return;
}
int main()
{
ios::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
cin>>s;
init(n);
for(int i=0;i<n-1;i++)
{
ll a,b;
cin>>a>>b;
a--;
b--;
g[a].push_back(b);
g[b].push_back(a);
}
//odd
ll low = 0;
ll high = (n-1)/2;
while(low!=high)
{
ll mid=(low+high+1)/2;
if(centroid_decomposition(0,mid*2+1))
low = mid;
else
high = mid-1;
}
ans = 2*low+1;
//even
low = 0;
high = (n/2);
while(low!=high)
{
ll mid=(low+high+1)/2;
if(centroid_decomposition(0,mid*2))
low = mid;
else
high = mid-1;
}
ans = max(ans,low*2);
cout<<ans<<"\n";
}
