#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint1000000007;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

int N;
string S;

vector<vector<pair<int,char>>> E;

void dfs(int cur,int p,vector<vector<int>> &dp){
	dp[cur][0] = 0;
	char c = '0';
	rep(i,E[cur].size()){
		int to = E[cur][i].first;
		if(to==p){
			c = E[cur][i].second;
			continue;
		}
		dfs(to,cur,dp);
		
		rep(j,S.size()+1){
			dp[cur][j] = min(dp[cur][j],dp[to][j]);
		}
	}
	
	if(c!='0'){
		for(int i=S.size()-1;i>=0;i--){
			if(dp[cur][i]==Inf)continue;
			for(int j=dp[cur][i];j<S.size();j++){
				if(S[j]==c){
					dp[cur][i+1] = min(dp[cur][i+1],j+1);
					break;
				}
			}			
		}
	}
}



int ans = 0;

using P = pair<int,int>;
using PP = pair<P,P>;
PP op(PP a,PP b){
	PP ret;
	array<P,5> A = {a.first,a.second,b.first,b.second,make_pair(-Inf,-1)};
	
	sort(A.rbegin(),A.rend());
	
	ret.first = A[0];
	for(int i=1;i<5;i++){
		if(A[0].second!=A[i].second){
			ret.second = A[i];
			break;
		}
	}
	return ret;
}

PP e(){
	return make_pair(make_pair(-Inf,-1),make_pair(-Inf,-1));	
}

void dfs(int cur,int p,vector<vector<int>> &dp,vector<vector<int>> &rdp){
	segtree<PP,op,e> seg(S.size()+1);
	
	rep(i,E[cur].size()){
		int to = E[cur][i].first;
		if(to==p)continue;
		dfs(to,cur,dp,rdp);
	}
	
	rep(i,E[cur].size()){
		int to = E[cur][i].first;
		if(to==p)continue;
		rep(j,dp[to].size()){
			if(dp[to][j]==Inf)continue;
			auto ret = seg.get(dp[to][j]);
			ret = op(ret,make_pair(make_pair(j,to),make_pair(-Inf,-1)));
			seg.set(dp[to][j],ret);
			ans = max(ans,j);
		}
	}
	
	rep(i,E[cur].size()){
		int to = E[cur][i].first;
		if(to==p)continue;
		rep(j,dp[to].size()){
			if(rdp[to][j]==Inf)continue;
			ans = max(ans,j);
			auto ret = seg.prod(0,(int)S.size() - rdp[to][j]+1);
			if(ret.first.second != to){
				ans = max(ans,j + ret.first.first);
			}
			if(ret.second.second != to){
				ans = max(ans,j + ret.second.first);
			}
		}
	}
	
}

int main(){
	
	cin>>N>>S;
	
	E.resize(N);
	
	rep(i,N-1){
		int u,v;
		char c;
		cin>>u>>v>>c;
		u--;v--;
		
		E[u].emplace_back(v,c);
		E[v].emplace_back(u,c);
	}
	
	vector dp(N,vector<int>(S.size()+1,Inf));
	vector rdp(N,vector<int>(S.size()+1,Inf));
	
	dfs(0,-1,dp);
	/*
	rep(i,N){
		rep(j,S.size()+1){
			cout<<dp[i][j]<<',';
		}
		cout<<endl;
	}*/
	
	
	reverse(S.begin(),S.end());
	
	dfs(0,-1,rdp);
	/*
	rep(i,N){
		rep(j,S.size()+1){
			cout<<rdp[i][j]<<',';
		}
		cout<<endl;
	}*/
	
	dfs(0,-1,dp,rdp);
	
	cout<<ans<<endl;
	
    return 0;
}