using System;

using System.Linq;

using System.Text.RegularExpressions;

using System.Globalization;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var list = new [] {

            "1.one",

            "2. two",

            "no number",

            "2.duplicate",

            "300. three hundred",

            "4-ignore this"};

        var regex = new Regex(@"^\d+(?=\.)", RegexOptions.Compiled);

        list.Select(i => {

            var m = regex.Match(i);

            return new KeyValuePair<int, string>( m.Success ? Int32.Parse(m.Value) : -1, i );

        })

        .Where(i => i.Key > -1)

        .GroupBy(i => i.Key)

        .Select(g => g.First().Value)

        .ToList().ForEach(Console.WriteLine);

    }

}