Code for the "Simple Text Editor" challenge on hackerrank.com

[hackerrank]_Simple_Text_Editor.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Text;

class Operation 
{
    protected readonly Stack<Operation> operationStack;
    protected readonly string context;

    public Operation(Stack<Operation> operationStack, string ctx) 
    {
        this.operationStack = operationStack;
        this.context = ctx;
    }
    
    public bool IgnoreOperation { get; set; } = false;
    
    public virtual string Execute(string input) 
    {
        return this.context;
    }
    
    public string Undo() 
    {
        return this.context;
    }
}

class AppendOperation : Operation 
{
    public AppendOperation(Stack<Operation> operationStack, string ctx) : base(operationStack, ctx) {}
    
    public override string Execute(string input) 
    {
        return this.context + input;
    }
}

class DeleteOperation : Operation 
{
    public DeleteOperation(Stack<Operation> operationStack, string ctx) : base(operationStack, ctx) {}
    
    public override string Execute(string input) 
    {
        int nbToDelete = Convert.ToInt32(input);
        return this.context.Substring(0, this.context.Length - nbToDelete);
    }
}

class PrintOperation : Operation {
    public static StringBuilder output = new StringBuilder();
    
    public PrintOperation(Stack<Operation> operationStack, string ctx) : base(operationStack, ctx) 
    {
        this.IgnoreOperation = true;
    }
    
    public override string Execute(string input) 
    {
        int indexToPrint = Convert.ToInt32(input) - 1;
        output.AppendLine(this.context[indexToPrint].ToString());
        
        return this.context;
    }
}

class UndoOperation : Operation 
{
    public UndoOperation(Stack<Operation> operationStack, string ctx) : base(operationStack, ctx) 
    {
        this.IgnoreOperation = true;
    }
    
    public override string Execute(string input) 
    {
        Operation lastAction = this.operationStack.Pop();
        return lastAction.Undo();
    }
}

class Solution 
{
    static void Main() 
    {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        Stack<Operation> operations = new Stack<Operation>();
        string ctx = string.Empty;
        
        int n = Convert.ToInt32(Console.ReadLine());
        for (int i = 0; i < n; i++) {
            string[] args = Console.ReadLine().Split(' ');
            
            Operation operation = null;
            switch (args[0]) {
                case "1":
                    operation = new AppendOperation(operations, ctx);
                    break;
                case "2":
                    operation = new DeleteOperation(operations, ctx);
                    break;
                case "3":
                    operation = new PrintOperation(operations, ctx);
                    break;
                case "4":
                    operation = new UndoOperation(operations, ctx);
                    break;
            }
            
            ctx = operation.Execute(args.Length > 1 ? args[1] : null);
            if (!operation.IgnoreOperation)
                operations.Push(operation);
        }
        
        Console.WriteLine(PrintOperation.output.ToString());
    }
}