Solution Review: Finding the First Unique Integer in an Array

namespace chapter_2
{
    class Challenge_6
    {
        //Find First Unique Integer in an Array
        //Returns first unique integer from array
        static int findFirstUnique(int []arr, int size)
        {
            //Inside the inner loop, check each index of the outer loop. 
            //If it's repeated in the array
            //If it's not repeated then return this as the first unique integer
            bool isRepeated = false;
            for (int i = 0; i < size; i++)
            {
                for (int j = 0; j < size; j++)
                {
                    if (arr[i] == arr[j] && i != j)
                    {
                        isRepeated = true;
                    }
                } //end of InnerLoop
                if (isRepeated == false)
                {
                    return arr[i];
                }
                isRepeated = false;
            } //end of OuterLoop
            return -1;
        }
        static void Main(string[] args)
        {
            int size = 6;
            int []arr = { 2, 54, 7, 2, 6, 54 };
            Console.Write( "Array: ");
            for (int i = 0; i < size; i++)
                Console.Write( arr[i] + " ");
            Console.WriteLine("");
            int unique = findFirstUnique(arr, size);
            Console.WriteLine ("First Unique in an Array: " + unique );
            return ;
        }
    }
}