using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace ConsoleApplication1
{
    public class Program
    {
        static object obj = new object();
        static int bilans = 1100;
        static void Main(string[] args)
        {
            Thread t1 = new Thread(new ThreadStart(Dodaj));
            Thread t2 = new Thread(new ThreadStart(Odejmij));
            t1.Start();
            t2.Start();

        }

        static void Dodaj()
        {
            lock (obj)
            {

                for (int i = 1; i <= 20; i++)
                {
                    lock (obj)
                    {
                        bilans += 100;
                        Console.WriteLine(bilans);
                    }
                }
            }
        }


        static void Odejmij()
        {
            lock (obj)
            {

                for (int i = 1; i <= 20; i++)
                {
                    lock (obj)
                    {
                        bilans -= 100;
                        Console.WriteLine(bilans);
                    }
                }
            }
            Console.ReadKey();
        }

    }
}