using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(firstNonRepeatingChar("Tofeeto"));

    }

​

​

    public static char firstNonRepeatingChar(string word)

    {

        List<char> repeating = new List<char>();

        List<char> nonRepeating = new List<char>();

        word = word.ToLower();

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

        {

            char letter = word[i];

            if (repeating.Contains(letter))

            {

                continue;

            }

            if (nonRepeating.Contains(letter))

            {

                nonRepeating.Remove((char) letter);

                repeating.Add(letter);

            }

            else

            {

                nonRepeating.Add(letter);

            }

        }

        return nonRepeating[0];

    }

}

​