Help me find a mistake

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace курсач_1196
{
    class Program
    {
        static void Main(string[] args)
        {
            int n1 = int.Parse(Console.ReadLine());
            int[] a = new int[n1];
            for (int i = 0; i < n1; i++)
                a[i] = int.Parse(Console.ReadLine());
            int n2 = int.Parse(Console.ReadLine());
            int[] b = new int[n2];
            for (int j = 0; j < n2; j++)
                b[j] = int.Parse(Console.ReadLine());
            Array.Sort(a);
            int[] ab = a.Intersect(b).ToArray();
            Console.WriteLine(ab.Length);

        }
    }
}