using System;

using System.Diagnostics;

using System.Threading.Tasks;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static async Task Main()

    {

        var stopwatch = Stopwatch.StartNew();

        await foreach (var pair in First().Zip(Second()))

            Console.WriteLine(pair);

        Console.WriteLine($"Duration: {stopwatch.ElapsedMilliseconds:#,0} msec");

​

        static async IAsyncEnumerable<int> First()

        {

            for (int i = 1; i <= 5; i++) { await Task.Delay(100); yield return i; }

        }

        static async IAsyncEnumerable<int> Second()

        {

            for (int i = 1; i <= 5; i++) { await Task.Delay(100); yield return i; }

        }

    }

}