using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var data = new []{

            new List<decimal> { 5.3M, 5.1M, 4.2M, 4.1M, 1.1M, }, 

            new List<decimal> { 5.3M, 5.1M, 3.2M, 4.1M, 1.1M, }, 

            new List<decimal> { 1.0M, 5.3M, 4.1M, 3.2M, 4.3M, 1.1M, }, 

            new List<decimal> { 5.3M, 4.1M, 3.2M, 4.3M, 1.1M, }, 

            new List<decimal> { 5.3M, 4.1M, 3.2M, 3.5M, }, 

            new List<decimal> { 5M, 2M, 4M, 3M, 1M, 2M, 1M}, 

        };

        foreach(var s in data){

            Console.WriteLine("input:  " + string.Join(", ",s));

            var r = RemoveIllegal(s);

            Console.WriteLine("output: " + string.Join(", ",r));

            Console.WriteLine("-------------------------------------");

        }

    }

    private static List<decimal> RemoveIllegal(List<decimal> source)

    {

        var candidates = new Stack<List<decimal>>();

        candidates.Push(source);

​

​

        var result = default(List<decimal>);

​

        while (candidates.TryPop(out var currentCandidate))

        {

            var prev = currentCandidate[0];

            var index = 1;

            while (index < currentCandidate.Count)

            {

                var curr = currentCandidate[index];

                if (prev < curr)

                {

                    var newCandidate = new List<decimal>(currentCandidate);

                    newCandidate.RemoveAt(index);

                    candidates.Push(newCandidate);

​

                    while (index > 0 && currentCandidate[index-1]< currentCandidate[index])

                    {

                        currentCandidate.RemoveAt(index - 1);

                        index--;

                    }

                }

​

                prev = curr;

                index++;

            }

​

            if (result == null)

            {

                result = currentCandidate;

            }

            else {

                result = currentCandidate.Count > result.Count ? currentCandidate : result;

            }

        }

​

        return result;

    }

}