#include <bits/stdc++.h>
#define inf 2e9
#define pb push_back
#define all(v) v.begin(), v.end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair <int, int> pii;
const int N = 50000 + 3, P = 31;
int n;
vector <int> v[N];
string s;
ull h[3002][3002];
int dst[3002][3002];
ull hs[N], deg[N];
ull rhs[N], rdeg[N];
void dfs(int st, int x, int pr){
if (x == st) h[x][x] = s[x] - 'a' + 1, dst[x][x] = 0;
for (auto u: v[x]){
if (u == pr) continue;
dst[st][u] = dst[st][x] + 1;
h[st][u] = h[st][x] * P + (s[u] - 'a' + 1);
dfs(st, u, x);
}
}
void solve1(){
for (int i = 0; i < n; i++)
dfs(i, i, -1);
int mx = 0;
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++)
if (h[i][j] == h[j][i]){
mx = max(mx, dst[i][j]);
}
cout << mx + 1;
return;
}
void prec(){
hs[0] = s[0] - 'a' + 1;
deg[0] = 1;
for (int i = 1; i < s.size(); i++){
hs[i] = hs[i - 1] * P + s[i] - 'a' + 1;
deg[i] = deg[i - 1] * P;
}
reverse(all(s));
rhs[0] = s[0] - 'a' + 1;
rdeg[0] = 1;
for (int i = 1; i < s.size(); i++){
rhs[i] = rhs[i - 1] * P + s[i] - 'a' + 1;
rdeg[i] = rdeg[i - 1] * P;
}
reverse(all(s));
}
ull get_rh(int l, int r){
l = n - 1 - l;
r = n - 1 - r;
swap(l, r);
if (!l) return rhs[r];
return rhs[r] - rhs[l - 1] * rdeg[r - l + 1];
}
ull get_h(int l, int r){
if (!l) return hs[r];
return hs[r] - hs[l - 1] * deg[r - l + 1];
}
bool is_pal(int l, int r){
if (l > r) return false;
return get_h(l, r) == get_rh(l, r);
}
void solve2(){
int ans = 1;
for (int i = 0; i < n; i++){
int l = 0, r = min(i, n - i - 1) + 1;
while (l < r){
int mid = (l + r) / 2;
if (is_pal(i - mid, i + mid)) l = mid + 1;
else r = mid;
}
--l;
ans = max(ans, l * 2 + 1);
}
for (int i = 1; i < n; i++){
int l = 0, r = min(i, n - i) + 1;
while (l < r){
int mid = (l + r) / 2;
if (is_pal(i - mid, i + mid - 1)) l = mid + 1;
else r = mid;
}
--l;
ans = max(ans, l * 2);
}
cout << ans;
return;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
#endif // LOCAL
cin >> n >> s;
prec();
for (int i = 0; i < n - 1; i++){
int x, y;
cin >> x >> y;
--x; --y;
v[x].pb(y);
v[y].pb(x);
}
// cout << get_h(2, 4) << " " << get_rh(2, 4) << "!\n";
// return 0;
if (n <= 3000){
solve1();
}else{
solve2();
}
}
