using System;
using static System.Console;
using System.Threading;
using System.Threading.Tasks;
using System.Diagnostics;

public class data{public int a,b; public double sum;};

public class main{

public static void hsum(object o){
	data d=(data)o;
	d.sum=0;
	for(int i=d.a;i<d.b;i++)d.sum+=1.0/i;
Write($"\thsum: from {(float)d.a} to {(float)d.b} is {(float)d.sum}\n");
	}

public static void Main(string[] args){
	int N=(int)1e8;
	if(args.Length>0)N=(int)double.Parse(args[0]);
	WriteLine($"N={(float)N}");
	var data1=new data();
	var data2=new data();
	data1.a=1;
	data1.b=N/2;
	data2.a=N/2;
	data2.b=N;
	Thread t = new Thread(hsum);
	var watch=new Stopwatch();
	watch.Reset();
	watch.Start();
Write($"Running hsum in 2 threads in parallel:\n");
	t.Start(data1);
	hsum(data2);
	t.Join();
	watch.Stop();
	double sum=data1.sum+data2.sum;
Write($"\tMain: hsum from {1} to {(float)N} is {(float)sum}\n");
Write($"\ttime: {watch.ElapsedMilliseconds/1000.0} sec\n");
	data2.a=1;
	data2.b=N;
	watch.Reset();
	watch.Start();
Write($"Running hsum in 1 thread:\n");
	hsum(data2);
Write($"\ttime: {watch.ElapsedMilliseconds/1000.0} sec\n");
	data2.sum=0;
Write($"Calculating sum in 4 threads via Parallel.For:\n");
	watch.Reset();
	watch.Start();
	Parallel.For<double>(
		1,N,()=>0.0,(i,loop,psum)=>psum+=1.0/i,
		(psum)=>{lock(data2);data2.sum+=psum;}
		);
	watch.Stop();
Write($"\tMain: hsum from {1} to {(float)N} is {(float)data2.sum}\n");
Write($"\ttime: {watch.ElapsedMilliseconds/1000.0} sec\n");
}//Main

}//class main