#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)
using ll = long long;
#define all(p) p.begin(),p.end()
const int mod=998244353;
int main(){
	int N;
	cin>>N;
	string S;
	cin>>S;
	vector<vector<pair<int,char>>> G(N);
	rep(i,0,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<int> order={0},pare(N,-1);
	pare[0]=-2;
	rep(i,0,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;
	int M=S.size();
	vector<string> T={S};
	reverse(all(S));
	T.push_back(S);
	vector<vector<vector<int>>> dp(2,vector<vector<int>>(N,vector<int>(M+1)));
	for(int po=N-1;po>=0;po--){
		int a=order[po];
		for(auto x:G[a]){
			if(pare[x.first]!=a) continue;
			rep(i,0,2){
				vector<int> n_dp(M+1);
				rep(j,0,M){
					if(x.second==T[i][j]){
						n_dp[j+1]=dp[i][x.first][j]+1;
					}
				}
				rep(j,1,M+1){
					dp[i][x.first][j]=max(n_dp[j],dp[i][x.first][j-1]);
				}
			}
			rep(i,0,2){
				rep(j,0,M+1) ans=max(ans,dp[i][a][j]+dp[1-i][x.first][M-j]);
			}
			rep(i,0,2){
				rep(j,0,M+1) dp[i][a][j]=max(dp[i][a][j],dp[i][x.first][j]);
			}
		}
	}
	cout<<ans<<"\n";
}