#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#define _GLIBCXX_DEBUG
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
ll ILL=2167167167167167167;
const int INF=2100000000;
const ll mod=998244353;
#define rep(i,a) for (int i=0;i<a;i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}


void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,t) solve();
}

void solve(){
	int N;
	cin>>N;
	string S;
	cin>>S;int M=S.size();
	vector<vector<pair<int,char>>> G(N);
	rep(i,N-1){
		int a,b;
		char c;
		cin>>a>>b>>c;
		a--,b--;
		G[a].push_back({b,c});
		G[b].push_back({a,c});
	}
	vector<vector<int>> dp1(N,vector<int>(M+1));
	vector<vector<int>> dp2(N,vector<int>(M+1));
	vector<int> order={0},pare(N,-1);
	pare[0]=-2;
	rep(i,N){
		int a=order[i];
		for(auto x:G[a]){
			if(pare[x.first]==-1){
				pare[x.first]=a;
				order.push_back(x.first);
			}
		}
	}
	int ans=0;
	for(int i=N-1;i>=0;i--){
		int a=order[i];
		for(auto x:G[a]){
			if(pare[x.first]==a){
				rep(j,M){
					if(x.second==S[j]){
						chmax(dp1[a][j+1],dp1[x.first][j]+1);
					}else{
						chmax(dp1[a][j+1],max(dp1[a][j],dp1[x.first][j+1]));
					}
				}
				for(int j=M-1;j>=0;j--){
					if(x.second==S[j]){
						chmax(dp2[a][j],dp2[x.first][j+1]+1);
					}else{
						chmax(dp2[a][j],max(dp2[a][j+1],dp2[x.first][j]));
					}
				}
			}
		}
	}
	rep(i,N){
		rep(j,M+1){
			int X=0,Y=0,x_ind=-1,y_ind=-2;
			int A=0,B=0,a_ind=-1,b_ind=-2;
			for(auto x:G[i]){
				if(pare[x.first]==i){
					if(chmax(Y,dp1[x.first][j])){
						y_ind=x.first;
						if(Y>X) swap(x_ind,y_ind),swap(X,Y);
					}
					if(chmax(B,dp2[x.first][j])){
						b_ind=x.first;
						if(B>A) swap(a_ind,b_ind),swap(A,B);
					}
				}
			}
			if(x_ind!=a_ind) chmax(ans,X+A);
			else chmax(ans,max(X+B,Y+A));
		}
	}
	chmax(ans,max(dp1[0][M],dp2[0][0]));
	cout<<ans<<"\n";
	/*rep(i,N){
		vec_out(dp1[i]);
		vec_out(dp2[i]);
		cout<<"\n";
	}*/
}