#include <bits/stdc++.h>
using namespace std;

class UnionFind{
    private:
    vector<int> par,siz;
    public:
    UnionFind(int N){
        par.resize(N,-1);
        siz.resize(N,1);
    }
 
    int root(int x){ //連結成分の代表頂点を返す.
        if(par.at(x) == -1) return x;
        else return par.at(x) = root(par.at(x));
    }
    bool unite(int u, int v){ //u,vを連結する 連結してた->false,した->trueを返す.
        u = root(u),v = root(v);
        if(u == v) return false;
 
        if(siz.at(u) < siz.at(v)) swap(u,v); //Union by size.
        par.at(v) = u;
        siz.at(u) += siz.at(v);
        return true;
    }
    bool issame(int u, int v){ //同じ連結成分ならtrue.
        if(root(u) == root(v)) return true;
        else return false;
    }
    int size(int pos){return siz.at(root(pos));} //posの連結成分の大きさを返す.
};

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

    int N,M; cin >> N >> M;
    vector<int> A(2*N+1);
    for(auto &a : A) cin >> a;

    int answer = M;
    vector<bool> already(2*N+1);
    vector<int> S(M);
    queue<int> Q;
    for(auto &s : S){
        cin >> s;
        already.at(s) = true,Q.push(s);
    }

    while(Q.size()){
        int t = Q.front(); Q.pop();
        for(auto s : S){
            if(s+t <= 2*N && already.at(A.at(s+t)) == false){
                already.at(A.at(s+t)) = true,Q.push(A.at(s+t)),answer++;
            }
        }
    }
    cout << answer << endl;

}