//thuanqvbn03
#include <bits/stdc++.h>
using namespace std;
const int MaxN = 50005;
struct LCA
{
int Time = 0;
int start[MaxN];
pair<int, int> RMQ[2 * MaxN][21];
void Start(int u, int Depth)
{
Time++;
start[u] = Time;
RMQ[Time][0] = make_pair(Depth, u);
}
void Add(int u, int Depth)
{
Time++;
RMQ[Time][0] = make_pair(Depth, u);
}
void Build()
{
int Log = log2(Time);
for (int t = 1; t <= Log; t++)
{
int j = (1 << (t - 1));
for (int i = Time - 2 * j + 1; i > 0; i--)
{
RMQ[i][t] = min(RMQ[i][t - 1], RMQ[i + j][t - 1]);
}
}
}
int Get(int u, int v)
{
u = start[u];
v = start[v];
if (u > v)
{
swap(u, v);
}
int Log = log2(v - u + 1);
return min(RMQ[u][Log], RMQ[v - (1 << Log) + 1][Log]).second;
}
};
int n;
string s;
vector<int> Adj[MaxN], aAdj[MaxN][26];
int depth[MaxN], Pd[MaxN];
int Ans;
LCA lca;
void DFS(int u)
{
lca.Start(u, depth[u]);
for (auto v : Adj[u])
{
if (v != Pd[u])
{
Pd[v] = u;
depth[v] = depth[u] + 1;
DFS(v);
lca.Add(u, depth[u]);
}
}
}
int dist(int u, int v)
{
return depth[u] + depth[v] - 2 * depth[lca.Get(u, v)];
}
void Solve(int u, int v)
{
int d = dist(u, v);
Ans = max(Ans, d);
for (int i = 0; i < 26; i++)
{
for (auto x : aAdj[u][i])
{
for (auto y : aAdj[v][i])
{
if (dist(x, y) == d + 2)
{
Solve(x, y);
}
}
}
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> s;
s = " " + s;
int u, v;
for (int i = 1; i < n; i++)
{
cin >> u >> v;
Adj[u].push_back(v);
Adj[v].push_back(u);
aAdj[u][s[v] - 'a'].push_back(v);
aAdj[v][s[u] - 'a'].push_back(u);
}
depth[1] = 0;
DFS(1);
lca.Build();
Ans = 0;
for (int i = 1; i <= n; i++)
{
Solve(i, i);
}
for (int i = 1; i <= n; i++)
{
for (auto j : Adj[i])
{
if (s[i] == s[j] && j != Pd[i])
{
Solve(i, j);
}
}
}
cout << Ans + 1;
return 0;
}
