#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define ll long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define repl(i,a,b) for(ll i=(a);i<(b);i++)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

template <typename T> bool chmin(T &a,T b){if(a>b){a=b;return true;} return false;}
template <typename T> bool chmax(T &a,T b){if(a<b){a=b;return true;} return false;}


int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  int n,m; cin >> n >> m;
  vector<int> a(2*n+1),s(m);
  rep(i,0,2*n+1) cin >> a[i];
  rep(i,0,m) cin >> s[i];
  vector<bool> seen(n+1,false);
  vector<int> b;
  queue<int> que;
  for(auto x:s) b.push_back(x), que.push(x), seen[x]=true;
  while(!que.empty()){
    auto x=que.front();
    que.pop();
    for(auto y:b){
      if(!seen[a[x+y]]){
        seen[a[x+y]]=true;
        que.push(a[x+y]);
      }
    }
  }
  int ans=0;
  rep(i,0,2*n+1) if(seen[i]) ans++;
  cout << ans << "\n";
}