using System;

​

public class Program

{

    public static void Main()

    {

        var example1 = new[]{2, 2, 1};

        var example2 = new[]{4, 1, 2, 1, 2};

        var example3 = new[]{1};

        Console.WriteLine("Example 1: " + SingleNumber(example1));

        Console.WriteLine("Example 2: " + SingleNumber(example2));

        Console.WriteLine("Example 3: " + SingleNumber(example3));

    }

​

    public static int SingleNumber(int[] nums)

    {

        var a = nums[0];

        for (var i = 1; i < nums.Length; i++)

        {

            a ^= nums[i];

        }

​

        return a;

    }

}