using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
class MainClass
{
static void Main ()
{
ConcurrentStack cs = new ConcurrentStack();
cs.Push(1);
cs.Push(2);
int result;
cs.TryPeek(out result);
cs.TryPop(out result);
cs.Clear();
}
}