import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


int N;
string S;
int[] A, B;
char[] C;

int[][] G;
int[] us;
int[] pari;

void dfs(int u, int pi) {
  us ~= u;
  pari[u] = pi;
  foreach (i; G[u]) if (pi != i) {
    if (B[i] == u) {
      swap(A[i], B[i]);
    }
    dfs(B[i], i);
  }
}

void main() {
  try {
    for (; ; ) {
      N = readInt;
      S = readToken;
      A = new int[N - 1];
      B = new int[N - 1];
      C = new char[N - 1];
      foreach (i; 0 .. N - 1) {
        A[i] = readInt - 1;
        B[i] = readInt - 1;
        C[i] = readToken[0];
      }
      
      G = new int[][N];
      foreach (i; 0 .. N - 1) {
        G[A[i]] ~= i;
        G[B[i]] ~= i;
      }
      us = [];
      pari = new int[N];
      dfs(0, -1);
      
      const SLen = cast(int)(S.length);
      auto up = new int[][](N - 1, SLen + 1);
      auto dn = new int[][](N - 1, SLen + 1);
      foreach_reverse (u; us) {
        const i = pari[u];
        if (~i) {
          // start
          foreach (k; 0 .. SLen) {
            if (C[i] == S[k           ]) chmax(up[i][k], 1);
            if (C[i] == S[SLen - 1 - k]) chmax(dn[i][k], 1);
          }
          // trans
          foreach (k; 0 .. SLen) {
            chmax(up[i][k + 1], up[i][k]);
            chmax(dn[i][k + 1], dn[i][k]);
          }
          const j = pari[A[i]];
          if (~j) {
            foreach (k; 0 .. SLen + 1) {
              chmax(up[j][k], up[i][k]);
              chmax(dn[j][k], dn[i][k]);
            }
            foreach (k; 0 .. SLen) {
              if (C[j] == S[k           ]) chmax(up[j][k + 1], up[i][k] + 1);
              if (C[j] == S[SLen - 1 - k]) chmax(dn[j][k + 1], dn[i][k] + 1);
            }
          }
        }
      }
      debug {
        writeln("A = ", A);
        writeln("B = ", B);
        writeln("up = ", up);
        writeln("dn = ", dn);
      }
      
      int ans;
      foreach (u; us) foreach (k; 0 .. SLen + 1) {
        int[2] mxs = [0, 0];
        int[2] js = [-1, -1];
        foreach (i; G[u]) if (A[i] == u) {
          int tmp = up[i][k];
          int j = i;
          static foreach (h; 0 .. 2) {
            if (mxs[h] < tmp) {
              swap(mxs[h], tmp);
              swap(js[h], j);
            }
          }
        }
        foreach (i; G[u]) if (A[i] == u) {
          const mx = mxs[(js[0] != 0) ? 0 : 1];
          chmax(ans, mx + dn[i][SLen - k]);
        }
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}