#include <bits/stdc++.h>
using namespace std;
#define rep(i, n)  for(long long i=0;i<(long long)(n);i++)
#define REP(i,k,n) for(long long i=k;i<(long long)(n);i++)
#define pb emplace_back
#define lb(v,k) (lower_bound(all(v),(k))-v.begin())
#define ub(v,k) (upper_bound(all(v),(k))-v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T,vector<T>,greater<T>>
#define dame(a) {out(a);return 0;}
#define decimal cout<<fixed<<setprecision(15);
#define all(a) a.begin(),a.end()
#define rsort(a) {sort(all(a));reverse(all(a));}
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
typedef long long ll;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> PP;
typedef tuple<ll,ll,ll,ll> PPP;
using vi=vector<ll>;
using vvi=vector<vi>;
using vvvi=vector<vvi>;
using vvvvi=vector<vvvi>;
using vp=vector<P>;
using vvp=vector<vp>;
using vb=vector<bool>;
using vvb=vector<vb>;
const ll inf=1001001001001001001;
const ll INF=1001001001;
const ll mod=1000000007;
const double eps=1e-10;
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outp(T a){cout<<'('<<a.fi<<','<<a.se<<')'<<'\n';}
template<class T> void outvp(T v){rep(i,v.size())cout<<'('<<v[i].fi<<','<<v[i].se<<')';cout<<'\n';}
template<class T> void outvvp(T v){rep(i,v.size())outvp(v[i]);}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){rep(i,v.size())outv(v[i]);}
template<class T> bool isin(T x,T l,T r){return (l)<=(x)&&(x)<=(r);}
template<class T> void yesno(T b){if(b)out("yes");else out("no");}
template<class T> void YesNo(T b){if(b)out("Yes");else out("No");}
template<class T> void YESNO(T b){if(b)out("YES");else out("NO");}
template<class T> void outset(T s){auto itr=s.begin();while(itr!=s.end()){if(itr!=s.begin())cout<<' ';cout<<*itr;itr++;}cout<<'\n';}
void outs(ll a,ll b){if(a>=inf-100)out(b);else out(a);}
ll gcd(ll a,ll b){if(b==0)return a;return gcd(b,a%b);}
ll modpow(ll a,ll b){ll res=1;a%=mod;while(b){if(b&1)res=res*a%mod;a=a*a%mod;b>>=1;}return res;}

int main(){
    ll n;cin>>n;
    string s;cin>>s;
    ll m=s.size();
    vi v(m);
    rep(i,m)v[i]=s[i]-'a';
    vvp g(n);
    rep(i,n-1){
        ll a,b;char c;cin>>a>>b>>c;a--;b--;
        ll d=c-'a';
        g[a].pb(b,d);g[b].pb(a,d);
    }
    vvi dpl(n,vi(m+1)),dpr(n,vi(m+1));
    ll ans=0;
    function<void(ll,ll)> dfs=[&](ll i,ll p){
        vvi a(m+1),b(m+1);
        for(auto x:g[i])if(x.fi!=p){
            dfs(x.fi,i);
            vi tmpl=dpl[x.fi],tmpr=dpr[x.fi];
            rep(j,m)if(v[j]==x.se)chmax(tmpl[j+1],dpl[x.fi][j]+1);
            rep(j,m)if(v[j]==x.se)chmax(tmpr[j],dpr[x.fi][j+1]+1);
            rep(j,m)chmax(tmpl[j+1],tmpl[j]);
            for(int j=m-1;j>=0;j--)chmax(tmpr[j],tmpr[j+1]);
            rep(j,m+1)a[j].pb(tmpl[j]);
            rep(j,m+1)b[j].pb(tmpr[j]);
            rep(j,m+1)chmax(dpl[i][j],tmpl[j]);
            rep(j,m+1)chmax(dpr[i][j],tmpr[j]);
        }
        rep(j,m+1){
            ll k=a[j].size();
            rep(i,k)chmax(ans,a[j][i]);
            rep(i,k)chmax(ans,b[j][i]);
            vi l(k),r(k);
            rep(i,k-1)l[i+1]=max(l[i],a[j][i]);
            for(int i=k-1;i>0;i--)r[i-1]=max(r[i],a[j][i]);
            rep(i,k)chmax(ans,b[j][i]+max(l[i],r[i]));
        }
    };dfs(0,-1);
    // outvv(dpl);outvv(dpr);
    out(ans);
}