using System.Collections.Generic;
public static void Main()
Console.WriteLine("Hello World");
List<int> input = new List<int> { 1, 2, 3, 3, 4 };
List<int> output = input.Except(input.GroupBy(i => i).Where(g => g.Count() > 1).Select(g => g.Key)).ToList();
Console.WriteLine(string.Join("\n", output));