Encode and Decode Strings

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class Program
{
    static int[] Ria(string line = null)
    {
        line ??= Console.ReadLine();
        if (string.IsNullOrWhiteSpace(line)) return Array.Empty<int>();
        return line.Trim().Split(new[] { ' ', ',', '\t' }, StringSplitOptions.RemoveEmptyEntries)
            .Select(int.Parse).ToArray();
    }
    static string[] Rsa()
    {
        int n = int.Parse(Console.ReadLine());
        var arr = new string[n];
        for (int i = 0; i < n; i++) arr[i] = Console.ReadLine();
        return arr;
    }
    static void W(params object[] parts) => Console.WriteLine(string.Join(" ", parts));
    static void Wb(bool v) => Console.WriteLine(v ? "true" : "false");
    static void Wi(int v) => Console.WriteLine(v);
    static void Ws(string v) => Console.WriteLine(v);

    static void Main()
    {
int n = int.Parse(Console.ReadLine());
var input = new string[n];
for (int i = 0; i < n; i++) input[i] = Console.ReadLine();
var sb = new StringBuilder();
foreach (var s in input) sb.Append(s.Length).Append('#').Append(s);
string encoded = sb.ToString();
var decoded = new List<string>();
int i2 = 0;
while (i2 < encoded.Length) {
    int j = encoded.IndexOf('#', i2);
    int len = int.Parse(encoded.Substring(i2, j - i2));
    decoded.Add(encoded.Substring(j + 1, len));
    i2 = j + 1 + len;
}
Ws(string.Join(",", decoded));
    }
}