using System;

​

public class Program

{

    public static void Main()

    {

        var A = new int[]{9, 2, 9, 3, 9, 3, 9};

        Console.WriteLine("Result {0}", OddOccurancesInArray(A));

    }

​

    static int OddOccurancesInArray(int[] A)

    {

        var i = 0;

        while (i <= A.GetUpperBound(0))

        {

            var n = A[i];

            var j = Array.IndexOf(A, n, ++i);

            if (j == -1)

                return n;

            A[j] = A[i++];

        }

​

        return -1;

    }

}