using System;

public class Program

{

    public static void Main()

    {

        int[] array = new int []{9,3,9,3,9,7,9};

        for(int i = 0; i < array.Length; i++){

            Console.Write(array[i] +", ");

        }

        int res  = solution(array);

        Console.WriteLine(res);

        res = 0;

        for(int i = 0; i < array.Length; i++){

            res = res ^ array[i]; 

        }

        Console.WriteLine(res);

    }

    public static int solution(int[] A) {

        for(int i = 0; i< A.Length; i++){

            int numToCompare = A[i];

            for(int j = i+1; j< A.Length; j++){

                if(A[i] == -1){

                    continue;

                }

                else if(A[i] == A[j]){

                    A[i] = A[j] = -1; //Mark as paired

                }

            }

        }

        int num = 0;

        for(int i = 0; i < A.Length; i++){

            if(A[i] != -1){

                num = A[i];

            }

        }

        return num;

    }

}