using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

            List<string> lstNumbs = new List<string>() {"f", "d", "7", "4", "5", "4", "2"};

​

            var result = lstNumbs.Where(c => Int32.TryParse(c, out int _)).Select(s => s);

​

            foreach (var item in result)

            {

                Console.WriteLine(item);

            }

    }

}