#include<bits/stdc++.h>
using namespace std;
string S;
vector<int> adj[50100];
int pw[50100];
int I, ans = 0;
void dfs(int x, int len, long long h, long long h2, int p) {
h = (h*27+S[x-1]-'a'+1)%99999999999999997;
h2 = (h2+pw[len-1]*(S[x-1]-'a'+1))%99999999999999997;
if(h==h2) {
ans = max(ans, len);
}
for(auto i: adj[x])
if(i!=p)
dfs(i,len+1,h, h2,x);
}
int main() {
pw[0] = 1;
for(int i = 1; i <= 50000; i++)
pw[i] = pw[i-1]*27%99999999999999997;
int n;
cin >> n >> S;
for(int i = 1; i < n; i++) {
int a, b;
cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
for(I = 1; I <= n; I++) {
dfs(I,1,0,0,0);
}
cout << ans << '\n';
}
