Main.cs

using System;
using System.Linq;
using System.Collections.Generic;

class Program
{
  static void Main(string[] args)
  {
    var num = Enumerable.Range(-5, 6);
    
    Console.WriteLine(num.FirstOrDefault(item => item < 1));
    Console.WriteLine(num.LastOrDefault(item => item < 2));
    Console.WriteLine(num.Where(item => item < 0).ElementAt(2));
  }
}