Algorithm to remove duplicate characters from a string: C#

Algorithm to remove duplicate characters from a string: C#

class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Enter the String");
            string inp = Console.ReadLine();
          
            string du = RemoveDuplicates(inp);
            Console.WriteLine(du);
            Console.ReadKey();
        }

        static string RemoveDuplicates(string input)
        {
            StringBuilder result=new StringBuilder();
            char[] chars = input.ToCharArray();
           
            for(int i=0;i<chars.Length;i++)
            {
                int counter = 0;
                for (int j=i+1; j<chars.Length;j++)
                {
                   
                    if (chars[i] == chars[j])
                        counter++;
                }
                if(counter<1)
                result.Append(chars[i]);
            }
            return result.ToString();
        }
    }

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