using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using System.Runtime.CompilerServices;

internal static class Program
{
    private static async System.Threading.Tasks.Task Main(string[] args)
    {
        await foreach (int count in CountsAsync(CancellationToken.None)) Console.WriteLine($"Count: {count}");
    }

    internal static async IAsyncEnumerable<int> CountsAsync([EnumeratorCancellation] CancellationToken token = default)
    {
        foreach (int count in new[] { 2, 4 })
        {
            token.ThrowIfCancellationRequested();
            await Task.Yield();
            yield return count;
        }
    }
}