Solution Review: Find First Unique Integer in an Array

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace chapter_9
{
    class challenge_7
    {
        static int findFirstUnique(int[] arr, int size)
        {
            Dictionary<int, int> MP = new Dictionary<int, int>();  // createing hash map
            for (int i = 0; i < size; i++)
            {
                if (MP.ContainsKey(arr[i]))
                {
                    MP[arr[i]]++;     // inserting elements in hash map
                }
                else
                {
                    MP[arr[i]] = 1;
                }
               
            }
                
            for (int i = 0; i < size; i++)
                if (MP[arr[i]] == 1)     // if value is equal to 1
                    return arr[i];     // return that element
            return -1;
        }
        static void Main(string[] args)
        {
            int[] arr = { -2, 5, -7, 6, 5, -2 };
            Console.Write("Array: ");
            for (int i = 0; i < arr.Length; i++)
                Console.Write(arr[i] + " ");
            Console.WriteLine("");
            int unique = findFirstUnique(arr, arr.Length);
            Console.WriteLine("First Unique in an Array: " + unique);
        }
    }
}