Stuck Numbers

using System;
using System.Linq;

class StuckNumbers
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        string[] input = Console.ReadLine().Split(' ').ToArray();
        //int[] numbers = new int[n];
        //for (int i = 0; i < numbers.Length; i++)
        //{
        //    numbers[i] = int.Parse(input[i]);
        //}
        bool isPrint = false;
        for (int a = 0; a < n; a++)
        {
            for (int b = 0; b < n; b++)
            {
                for (int c = 0; c < n; c++)
                {
                    for (int d = 0; d < n; d++)
                    {
                        if (a != b && a != c && a != d &&
                            b != c && b != d && c != d)
                        {
                            string first = input[a] + input[b];
                            string second = input[c] + input[d];
                            if (first == second)
                            {
                                Console.WriteLine("{0}|{1}=={2}|{3}", input[a], input[b], input[c], input[d]);
                                isPrint = true;
                            }
                        }
                    }
                }
            }
        }
        if (isPrint == false)
        {
            Console.WriteLine("No");
        }
    }
}