set<char>st;
    ll n; cin>>n;
  string s; cin>>s;
  ll x; cin>>x;
  vector<int>v;
  while(x--){
      char z; cin>>z;
      st.emplace(z);
  }
  for(auto i = st.begin(); i!= st.end(); i++){
      v.push_back(s.rfind(*i));
  }
  sort(rall(v));
  int differ;
  if(sz(v) == 1){
      if(v[0]<=0) {
      cout<<0<<nl;
        return;
      }else cout<<v[0]<<nl;
  }
  for(int i=0; i<sz(v)-1;i++){
    differ = v[i]-v[i+1];
  }
  differ = min(differ,v[sz(v)-1]);

// for(auto&h:v) cout<<h<<' ';

cout<<nl;