#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
// disable assert
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
using namespace std;
using ll = long long;
const ll INF = 1ll << 60;
#define REP(i,n) for(ll i=0; i<ll(n); i++)
template <class T> using V = vector<T>;
template <class A, class B> void chmax(A& l, const B& r){ if(l < r) l = r; }
template <class A, class B> void chmin(A& l, const B& r){ if(r < l) l = r; }

void testcase(){
    ll N, M; cin >> N >> M;
    V<ll> S(M), T(M);
    V<ll> A(N*2+1); REP(i,N*2+1) cin >> A[i];
    V<ll> vis(N+1);
    REP(i,M) cin >> S[i];
    T = S;
    for(auto a : S) vis[a] = 1;
    REP(i,T.size()){
        ll v = T[i];
        for(auto s : S) if(vis[A[s+v]] == 0){
            vis[A[s+v]] = 1;
            T.push_back(A[s+v]);
        }
    }
    cout << T.size() << "\n";
}

int main(){
  cin.tie(0)->sync_with_stdio(0);
  testcase();
  return 0;
}