using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var numbers = new[]{30, 20, 40};

        var number = 25;

        var closest = numbers.OrderBy(n => n).Cast<int ? >().FirstOrDefault(n => n >= number) ?? numbers.Last();

        Console.WriteLine(closest);

    }

}