using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        object obj=new object();

        double toplam=1;

        Parallel.For<double>(1,100000,

                     ()=>0,

                     (i,state,localtoplam)=>

                     {

                         if(i%2==0)

                         {

                             localtoplam+=(double)1/(i*2+1);

                         }else localtoplam-=(double)1/(i*2+1);

                     return localtoplam;

                     },

                     localtoplam=>{lock(obj) toplam+=localtoplam; }     

        );

        Console.WriteLine(toplam*=4);

    }

}