1using System;
2using System.Linq;
3
4class SpecialArray {
5    public int SpecialArrayFunc(int[] nums) {
6        Array.Sort(nums);
7        int n = nums.Length;
8        for (int x = 0; x <= n; x++) {
9            int count = nums.Count(num => num >= x);
10            if (count == x) {
11                return x;
12            }
13        }
14        return -1;
15    }
16
17    static void Main() {
18        SpecialArray sa = new SpecialArray();
19        int[] nums = {0, 4, 3, 0, 4};
20        Console.WriteLine(sa.SpecialArrayFunc(nums));
21    }
22}

1