❔ ✅ can anyone tell me what my problem is?

using System;
static class RandomLetter
{
    static Random _random = new Random();
    public static char GetLetter()
    {
        // This method returns a random lowercase letter.
        // ... Between 'a' and 'z' inclusive.
        int num = _random.Next(0, 25); // Zero to 25
        char let = (char)('a' + num);
        return let;
    }
}

class passwordgenerator
{
    public static void Main()
    {
        System.Random random = new System.Random();

        Console.WriteLine("enter wanted length:");
        var length = Console.ReadLine();
        var whentostop = 0;
        var slength = length.ToString();
        var swhentostop = whentostop.ToString();

        var password = "";

        while (true)
        {
            var letter = RandomLetter.GetLetter();
            var number = random.Next(0, 9);
            var NoM = random.Next(0, 4);

            if (NoM <= 2)
            {
                password += number;
                whentostop++;
            }
            if (NoM >= 3)
            {
                password += letter;
                whentostop++;
            }
            if (swhentostop == slength)
            {
                Console.WriteLine($"password generated is {password}");
            }
        }
    }
}