import sys

# sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = (1 << 63)-1
# inf = (1 << 31)-1
# md = 10**9+7
md = 998244353

n = II()
s = [ord(c)-97 for c in SI()]
m = len(s)
to = [[] for _ in range(n)]
for _ in range(n-1):
    u, v, c = SI().split()
    u = int1(u)
    v = int1(v)
    c = ord(c)-97
    to[u].append((v, c))
    to[v].append((u, c))

parent, depth, vis = [-1]*n, [0]*n, [0]*n
cc = [""]*n

def dfs(root):
    uu = []
    vis[root] = 1
    stack = [root]
    while stack:
        iu = stack.pop()
        i, u = divmod(iu, n)
        if i == 0:
            uu.append(u)
        # care to's format
        while i < len(to[u]) and vis[to[u][i][0]]: i += 1
        if i < len(to[u]):
            stack.append((i+1)*n+u)
            # care to's format
            v, c = to[u][i]
            vis[v] = 1
            stack.append(v)
            parent[v] = u
            depth[v] = depth[u]+1
            cc[v] = c

    return uu

uu = dfs(0)

def dodp(s):
    def chmax(i, j, val):
        if val > dp[i][j]: dp[i][j] = val

    dp = [[0]*(m+1) for _ in range(n)]
    for u in uu[::-1]:
        if u == 0: break
        if len(to[u]) == 1:
            for i, c in enumerate(s):
                if c == cc[u]:
                    dp[u][i+1] = 1
                    break
        p = parent[u]
        for i in range(m+1):
            pre = dp[u][i]
            if i < m and cc[p] == s[i]:
                chmax(p, i+1, pre+1)
            elif pre:
                chmax(p, i, pre)
                if i+1 <= m: chmax(u, i+1, pre)

    return dp

dp = dodp(s)
rdp = dodp(s[::-1])
# pDB(rdp)

ans = 0
for u in range(n):
    for i in range(m+1):
        m1 = m2 = 0
        for v, _ in to[u]:
            if v == parent[u]: continue
            v1, v2 = dp[v][i], rdp[v][m-i]
            if v1+m2 > ans: ans = v1+m2
            if v2+m1 > ans: ans = v2+m1
            if v1 > m1: m1 = v1
            if v2 > m2: m2 = v2

print(ans)