#pragma GCC optimize("O3,unroll-loops")
#include <stdio.h>
#include <string.h>
#define N (50005)
#define M 1000000007
#define fprintf(...) 42
#define EVEN 0x1
#define ODD 0x3
int dead[N], Base = 137, n, *eh[N], eo[N], Z[N + N], Z_, sz[N], answer = 1, mode, len, t1[N], t2[N], bp[1 + N], bpi[1 + N], ii, sentinel;
unsigned seed;
char s[N];
int bpow(int a, int b) {
if (!b) return 1;
int r = bpow(a, b / 2);
if (b & 1) return r * 1ll * r % M * a % M;
return r * 1ll * r %M;
}
int *rizz(int n) {
return Z + (Z_ += n) - n;
}
void init() {
bp[0] = 1;
for (int i = 1; i <= N; ++i)
bp[i] = bp[i - 1] * 1ll * Base % M;
for (int i = 0; i <= N; ++i)
bpi[i] = bpow(bp[i], M - 2);
static int u[N], v[N];
scanf("%d%s", &n, s + 1);
for (int i = 1; i < n; ++i) {
scanf("%d%d", &u[i], &v[i]);
++eo[u[i]]; ++eo[v[i]];
}
for (int i = 1; i <= n; ++i) {
eh[i] = rizz(eo[i]);
eo[i] = 0;
}
for (int i = 1; i < n; ++i) {
eh[u[i]][eo[u[i]]++] = v[i];
eh[v[i]][eo[v[i]]++] = u[i];
}
}
void dfs(int u, int p) {
sz[u] = 1;
for (int *v = eh[u]; eh[u] + eo[u] > v; ++v)
if (! dead[*v] && *v != p)
dfs(*v, u), sz[u] += sz[*v];
}
int get_centroid(int u, int p, int tsz) {
for (int *v = eh[u]; eh[u] + eo[u] > v; ++v)
if (! dead[*v] && *v != p && 2 * sz[*v] >= tsz)
return get_centroid(*v, u, tsz);
return u;
}
void centroid_reset() {
memset(dead, 0, sizeof dead);
ii = 0;
}
typedef unsigned Hash[31999999];
int has;
Hash mset[2];
int rrrr[2999999], records[2999999], ro;
void mset_insert(int o, int k) {
++ro;
rrrr[ro] = o;
records[ro] = k >> 5;
mset[o][k >> 5] |= 1 << (k & 31);
}
void mset_clear() {
while (ro)
{
mset[rrrr[ro]][records[ro]] = 0;
--ro;
}
}
int mset_count(int o, int k) {
return (mset[o][k >> 5] >> (k & 31)) & 1;
}
void upd(int *t, int p, int k) {
if (p)
t[p] = (t[p - 1] + k) % M;
else
t[p] = k % M;
}
int qry(int *t, int l, int r) {
if (l > r)
return 0;
if (l)
return (t[r] + (M - t[l - 1]) % M) % M;
return t[r];
}
void efs(int u, int p, int update, int dep) {
if (dep >= len)
return;
upd(t1, dep, (s[u] - 'Z' ) * 1ll * bp[dep] % M);
upd(t2, dep, (s[u] - 'Z' ) * 1ll * bp[N - dep] % M);
int y = len - dep;
int x = (dep - y) / 2;
if (mode == EVEN) {
if (update) {
if (dep * 2 < len) {
mset_insert(1, qry(t1, 0, dep));
} else {
if (x > 0 && qry(t1, 1, x) * 1ll * bpi[1] % M
!= qry(t2, x + 1, 2 * x) * 1ll * bpi[N - 2 * x] % M) {
}
else if (y > 1) {
mset_insert(0, qry(t1, 2 * x + 1, dep) * 1ll * bpi[2 * x + 1] % M);
}
else if ((s[u] - 'Z') == qry(t1, 0, 0))
++has;
}
} else {
if (dep * 2 < len) {
has += mset_count(0, qry(t1, 0, dep));
} else {
if (qry(t1, 1, x) * 1ll * bpi[1] % M
!= qry(t2, x + 1, 2 * x) * 1ll * bpi[N - 2 * x] % M) {
} else if (y > 1) {
has += mset_count(1, qry(t1, 2 * x + 1, dep) * 1ll * bpi[2 * x + 1] % M);
}
}
}
} else if (mode == ODD) {
if (update) {
if (dep * 2 + 1 == len) {
mset_insert(0, qry(t1, 0, dep));
} else if (dep * 2 < len) {
mset_insert(1, qry(t1, 0, dep));
} else {
if (x > 0 && qry(t1, 1, x) * 1ll * bpi[1] % M
!= qry(t2, x + 2, x + 2 + x - 1) * 1ll * bpi[N - 2 * x - 1] % M) {
}
else if (y > 1) {
mset_insert(0, qry(t1, 2 * x + 2, dep) * 1ll * bpi[2 * x + 2] % M);
}
else
if (s[u] - 'Z' == qry(t1, 0, 0)) {
++has;
}
}
} else {
if (dep * 2 + 1 == len) {
has += mset_count(0, qry(t1, 0, dep));
} else if (dep * 2 < len) {
has += mset_count(0, qry(t1, 0, dep));
} else {
if (qry(t1, 1, x) * 1ll * bpi[1] % M
!= qry(t2, x + 2, x + 2 + x - 1) * 1ll * bpi[N - 2 * x - 1] % M) {
}
else if (y > 1) {
has += mset_count(1, qry(t1, 2 * x + 2, dep) * 1ll * bpi[2 * x + 2] % M);
}
}
}
}
for (int *v = eh[u]; eh[u] + eo[u] > v; ++v)
if (! dead[*v] && *v != p)
efs(*v, u, update, dep + 1);
}
void centroid_decomposition(int u, int dep, int par) {
dfs(u, u);
u = get_centroid(u, u, sz[u]);
dead[u] = 1;
/* process */
upd(t1, 0, s[u] - 'Z');
upd(t2, 0, (s[u] - 'Z' ) * 1ll * bp[N - 0] % M);
for (int *v = eh[u]; eh[u] + eo[u] > v; ++v)
if (! dead[*v]) {
efs(*v, 0, 0, 1);
efs(*v, 0, 1, 1);
}
mset_clear();
/* decomp */
for (int *v = eh[u]; eh[u] + eo[u] > v; ++v)
if (! dead[*v])
centroid_decomposition(*v, dep + 1, u);
}
void find_even() {
mode = EVEN;
int lower = 0, upper = n / 2 + 1;
while (upper - lower > 1) {
int mid = lower + (upper - lower) / 2;
len = mid * 2;
has = 0;
centroid_reset();
centroid_decomposition(1, 0, 0);
if (has)
lower = mid;
else
upper = mid;
}
if (answer < lower * 2)
answer = lower * 2;
}
void find_odd() {
mode = ODD;
int lower = 1, upper = (n + 1) / 2 + 1;
while (upper - lower > 1) {
int mid = lower + (upper - lower) / 2;
len = mid * 2 - 1;
has = 0;
if (len <= answer)
has = 1;
else {
centroid_reset();
centroid_decomposition(1, 0, 0);
}
if (has)
lower = mid;
else
upper = mid;
}
if (answer < lower * 2 - 1)
answer = lower * 2 - 1;
}
int main() {
init();
find_even();
find_odd();
printf("%d\n", answer);
return 0;
}
