#include <stdio.h>
#include <stdlib.h>
#define N 50000
int abs_(int a) { return a > 0 ? a : -a; }
int max(int a, int b) { return a > b ? a : b; }
int *ej[N], eo[N];
void append(int i, int j) {
int o = eo[i]++;
if (o >= 2 && (o & o - 1) == 0)
ej[i] = (int *) realloc(ej[i], o * 2 * sizeof *ej[i]);
ej[i][o] = j;
}
char cc[N + 1]; int d_;
void dfs1(int p1, int i1, int p2, int i2, int d) {
int o1, o2;
d_ = max(d_, d);
for (o1 = eo[i1]; o1--; ) {
int j1 = ej[i1][o1];
for (o2 = eo[i2]; o2--; ) {
int j2 = ej[i2][o2];
if (j1 != p1 && j2 != p2 && (i1 != i2 || j1 < j2) && cc[j1] == cc[j2])
dfs1(i1, j1, i2, j2, d + 2);
}
}
}
int pp[N], dd[N];
void dfs2(int p, int i, int d) {
int o;
pp[i] = p, dd[i] = d;
for (o = eo[i]; o--; ) {
int j = ej[i][o];
if (j != p)
dfs2(i, j, d + 1);
}
}
int manacher(char *cc, int n) {
static char cc_[N * 2 + 2];
static int rr[N * 2 + 1];
int i, o, x, ans;
for (i = 0; i < n * 2 + 1; i++)
cc_[i] = i % 2 == 0 ? ' ' : cc[i / 2];
for (i = 0, o = 0, x = 0; i < n * 2 + 1; i++)
if (i < x && i + rr[o + o - i] < x)
rr[i] = rr[o + o - i];
else {
o = i, x = max(x, i);
while (x < n * 2 + 1 && o + o - x >= 0 && cc_[x] == cc_[o + o - x])
x++;
rr[i] = x - o;
}
ans = 0;
for (i = 0; i < n * 2 + 1; i++)
ans = max(ans, rr[i] - 1);
return ans;
}
int main() {
static int ii[N - 1], jj[N - 1], qu[N], qu1[N], qu2[N];
static char cc_[N + 1];
int n, h, h_, i, j, cnt, cnt1, cnt2;
scanf("%d%s", &n, cc);
for (i = 0; i < n; i++)
ej[i] = (int *) malloc(2 * sizeof *ej[i]);
for (h = 0; h < n - 1; h++) {
scanf("%d%d", &i, &j), i--, j--;
ii[h] = i, jj[h] = j;
append(i, j), append(j, i);
}
if (n <= 3000) {
for (i = 0; i < n; i++)
dfs1(-1, i, -1, i, 1);
for (h = 0; h < n - 1; h++)
if (cc[ii[h]] == cc[jj[h]])
dfs1(ii[h], jj[h], jj[h], ii[h], 2);
} else {
dfs2(-1, 0, 0);
cnt = 0;
for (i = 0; i < n; i++)
if (eo[i] == 1)
qu[cnt++] = i;
for (h = 0; h < cnt; h++)
for (h_ = h + 1; h_ < cnt; h_++) {
i = qu[h], j = qu[h_];
cnt1 = 0, cnt2 = 0;
while (i != j)
if (dd[i] > dd[j])
qu1[cnt1++] = i, i = pp[i];
else
qu2[cnt2++] = j, j = pp[j];
for (h = 0; h < cnt1; h++)
cc_[h] = cc[qu1[h]];
cc_[cnt1] = cc[i];
for (h = 0; h < cnt2; h++)
cc_[cnt1 + cnt2 - h] = cc[qu2[h]];
d_ = max(d_, manacher(cc_, cnt1 + 1 + cnt2));
}
}
printf("%d\n", d_);
return 0;
}
