using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string testCase = "jjxei";

        var answer = testCase.Where(charVal => CharCount(testCase.ToArray(), charVal) == 1).FirstOrDefault();

        Console.WriteLine(answer);

    }

    public static int CharCount(char[] arr, char c){

        return arr.Where(character => character == c).Count();

    }

}