[C#] 백준 5597번 : 과제 안 내신 분..?

[C#] 백준 5597번 : 과제 안 내신 분..?

using System;

class Program
{
    static void Main()
    {
        int[] numbers = new int[30];
        int[] students = new int[28];
        int[] absense = new int[2];

        int index = 0;

        for (int i = 0; i < 28; i++)
        {
            int stu = int.Parse(Console.ReadLine());
            students[i] = stu;
        }

        for (int t = 0; t < 30; t++)
        {
            numbers[t] = t + 1;
        }

        for (int j = 0; j < 30; j++)
        {
                if (Array.IndexOf(students, numbers[j]) == -1)
                {
                    absense[index++] = numbers[j];
                }
        }

        for (int t = 0; t < absense.Length; t++)
        {
            Console.WriteLine(absense[t]);
        }
    }
}