using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;
using System.Security.Cryptography;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, m) = (c[0], c[1]);
        var a = NList;
        var s = NList;
        var set = new HashSet<int>(s);
        var add = new HashSet<int>();
        for (var i = 0; i < s.Length; ++i) for (var j = i; j < s.Length; ++j) if (!set.Contains(a[s[i] + s[j]]))
        {
            set.Add(a[s[i] + s[j]]);
            add.Add(a[s[i] + s[j]]);
        }
        while (add.Count > 0)
        {
            var nadd = new HashSet<int>();
            foreach (var ai in add) for (var i = 0; i < s.Length; ++i) if (!set.Contains(a[ai + s[i]]))
            {
                set.Add(a[ai + s[i]]);
                nadd.Add(a[ai + s[i]]);
            }
            add = nadd;
        }
        WriteLine(set.Count);
    }
}