#include<bits/stdc++.h>
using namespace std;
#define ALL(x) begin(x),end(x)
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define mod 998244353
using ll=long long;
const int INF=1000000000;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0},dy[]={0,1,0,-1};
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}

// graph template
// ref : https://ei1333.github.io/library/graph/graph-template.cpp
template<typename T=int>
struct Edge{
    int from,to;
    T w;
    int idx;
    Edge()=default;
    Edge(int from,int to,T w=1,int idx=-1):from(from),to(to),w(w),idx(idx){}
    operator int() const{return to;}
};

template<typename T=int>
struct Graph{
    vector<vector<Edge<T>>> g;
    int V,E;
    Graph()=default;
    Graph(int n):g(n),V(n),E(0){}

    size_t size(){
        return g.size();
    }
    void resize(int k){
        g.resize(k);
    }
    inline const vector<Edge<T>> &operator[](int k)const{
        return (g.at(k));
    }
    inline vector<Edge<T>> &operator[](int k){
        return (g.at(k));
    }
    void add_directed_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E++);
    }
    void add_edge(int from,int to,T cost=1){
        g[from].emplace_back(from,to,cost,E);
        g[to].emplace_back(to,from,cost,E++);
    }
    void read(int m,int pad=-1,bool weighted=false,bool directed=false){
        for(int i=0;i<m;i++){
            int u,v;cin>>u>>v;
            u+=pad,v+=pad;
            T w=T(1);
            if(weighted) cin>>w;
            if(directed) add_directed_edge(u,v,w);
            else         add_edge(u,v,w);
        }
    }
};

template<typename T,typename GT=int>
struct Rerooting{
    using E=function<T(T,Edge<GT>)>;//集合，頂点番号
    using M=function<T(T,T)>;
    using F=function<T(T,int)>;
    
    Graph<GT> g;
    // dp_v = fix(merge(f(dp_c1,edge(v,c1)),...,f(dp_ck,edge(v,ck))),v)
    E f;    // f(T,Edge)->T  辺情報を考慮し，merge前の形
    M merge;// TxT->T，子を集約する関数，モノイド
    T e;    // mergeの単位元
    F fix;  // TxN->T  補正
    vector<vector<T>> dp;
    vector<T> ans;
    
    Rerooting(Graph<GT> &g,E f,M merge,T e,F fix=[](T a,int b){return a;}):
    g(g),f(f),merge(merge),e(e),fix(fix),dp(g.size()),ans(g.size(),e){}

    T dfs1(int pre,int now){
        T ret=e;
        for(int i=0;i<(int)g[now].size();i++)if(g[now][i]!=pre){
            dp[now][i]=dfs1(now,g[now][i]);
            ret=merge(ret,f(dp[now][i],g[now][i]));
        }
        return fix(ret,now);
    }
    void dfs2(int pre,int now,T frompar){
        for(int i=0;i<(int)g[now].size();i++){
            if(g[now][i]==pre){
                dp[now][i]=frompar;
                break;
            }
        }
        vector<T> lsum(g[now].size()+1),rsum(g[now].size()+1);//親も混ぜて累積
        lsum[0]=e;rsum[g[now].size()]=e;
        for(int i=0;i<(int)g[now].size();i++) lsum[i+1]=merge(lsum[i],f(dp[now][i],g[now][i]));
        for(int i=(int)g[now].size();i>0;i--) rsum[i-1]=merge(rsum[i],f(dp[now][i-1],g[now][i-1]));
        for(int i=0;i<(int)g[now].size();i++)if(g[now][i]!=pre){
            T fromme=merge(lsum[i],rsum[i+1]);
            dfs2(now,g[now][i],fix(fromme,now));
        }
    }
    void build(int root=0){
        for(int i=0;i<(int)g.size();i++) dp[i].resize(g[i].size());
        dfs1(-1,root);
        dfs2(-1,root,e);
        for(int i=0;i<(int)g.size();i++){
            for(int j=0;j<(int)g[i].size();j++) ans[i]=merge(ans[i],f(dp[i][j],g[i][j]));
            ans[i]=fix(ans[i],i);
        }
    }
};


vector<vector<int>> solve(Graph<char> &G,string S,vector<vector<int>> &nxt){
    cout<<"Hello "<<S<<endl;
    int N=G.V;
    int M=(int)S.size();
    vector<vector<int>> dp(N,vector<int>(M+1,0));

    function<void(int,int)> dfs=[&](int pre,int cur){
        for(auto &e:G[cur])if(e.to!=pre){
            dfs(cur,e.to);
            rep(j,M+1){
                chmax(dp[cur][j],dp[e][j]);
                int nj=nxt[j][e.w-'a'];
                if(nj<M) chmax(dp[cur][nj+1],dp[e.to][j]+1);
            }
        }
    };

    dfs(-1,0);
    return dp;
}




signed main(){
    int N;cin>>N;
    string S;cin>>S;
    Graph<char> G(N);
    G.read(N-1,-1,true);

    int M=(int)S.size();

    vector<vector<int>> nxt(M+1,vector<int>(26,M));
    for(int i=M-1;i>=0;i--){
        rep(j,26) nxt[i][j]=nxt[i+1][j];
        nxt[i][S[i]-'a']=i;
    }

    auto f=[&](vector<int> v,Edge<char> e){
        vector<int> ret(M+1,-INF);
        rep(i,M+1){
            int ni=nxt[i][e.w-'a'];
            chmax(ret[i],v[i]);
            if(ni<M) chmax(ret[ni+1],v[i]+1);
        }
        return ret;
    };
    auto merge=[&](vector<int> l,vector<int> r){
        rep(i,M+1) l[i]=max(l[i],r[i]);
        return l;
    };

    vector<int> e(M+1,-INF);
    e[0]=0;
    Rerooting<vector<int>,char> R(G,f,merge,e);

    R.build();
    int ans=0;
    rep(i,N)rep(j,M+1) chmax(ans,R.ans[i][j]);
    cout<<ans<<endl;
    return 0;
}