#include <bits/stdc++.h>
#define ll long long
#define F first
#define S second
#define MAXN 50005
#define ii pair<int,int>
#define bit(i,j) ((i>>j)&1)
#define sz(i) (int)i.size()
#define endl '\n'
using namespace std;
const int mod = 1e9 + 7, BASE = 31;
int n;
int a[MAXN];
vector<int>g[MAXN];
namespace sub1
{
bool ans ;
int sz[MAXN], h[MAXN];
int P[MAXN], up[MAXN], down[MAXN];
bool del[MAXN];
map<ll, bool>cnt[MAXN];
int dem(int u, int p)
{
int cnt = 1;
for(int v : g[u])
if(v != p && !del[v])
cnt += dem(v, u);
return sz[u] = cnt;
}
int centroid(int u, int p, int size)
{
for(int v : g[u])
if(v != p && !del[v] && sz[v] > size / 2)
return centroid(v, u, size);
return u;
}
void calc(int u, int p, int len)
{
h[u] = h[p] + 1;
if(h[u] > len)
return ;
down[u] = (1LL * down[p] * BASE % mod + a[u]) % mod;
up[u] = (1LL * a[u] * P[h[u] - 2] % mod + up[p]) % mod;
ll need = (1LL * up[u] * P[len - (h[u] - 1)] % mod - down[u] + mod) % mod;
if(cnt[len - h[u] + 1].find(need) != cnt[len - h[u] + 1].end())
return ans = 1, void();
for(int v : g[u])
if(v != p && !del[v])
calc(v, u, len);
}
void add(int u, int p, int len)
{
if(h[u] > len)
return ;
ll bu = (1LL * up[u] * P[len - h[u] + 1] % mod - down[u] + mod) % mod;
cnt[h[u]][bu] = 1;
for(int v : g[u])
if(v != p && !del[v])
add(v, u, len);
}
void dfs(int u, int len)
{
int size = dem(u, 0);
u = centroid(u, 0, size);
up[u] = 0;
down[u] = a[u];
h[u] = del[u] = 1;
cnt[1][(1LL * up[u]*P[len] % mod - down[u] + mod) % mod] = 1;
for(int v : g[u])
if(!del[v])
{
calc(v, u, len);
add(v, u, len);
}
for(int i = 1; i <= size; i++)
cnt[i].clear();
for(int v : g[u])
if(!del[v])
dfs(v, len);
}
bool check(int D)
{
ans = 0;
for(int i = 1; i <= n; i++)
del[i] = 0;
dfs(1, D);
return ans;
}
int bina(int l, int r, int p)
{
while(l < r)
{
int mid = (l + r + 1) / 2;
if(check(mid * 2 + p))
l = mid;
else
r = mid - 1;
}
return l * 2 + p;
}
void solve()
{
P[0] = 1;
for(int i = 1; i <= n; i++)
P[i] = 1LL * P[i - 1] * BASE % mod;
cout << max(bina(0, n / 2, 0), bina(0, (n - 1) / 2, 1));
}
}
main()
{
if(fopen("TEST.inp", "r"))
{
freopen("TEST.inp", "r", stdin);
freopen("TEST.out", "w", stdout);
}
ios_base::sync_with_stdio(0);
cin.tie(0);
string s;
cin >> n >> s;
for(int i = 1; i <= n; i++)
a[i] = s[i - 1] - 'a' + 1;
for(int i = 1; i < n; i++)
{
int x, y;
cin >> x >> y;
g[x].push_back(y);
g[y].push_back(x);
}
sub1::solve();
}
