void flick(int size=2000,int step=1000,int sleep=0)
{
	TFile *f = new TFile("flicker.root");
	TTree *pmvz = (TTree *)f->Get("pt");
   TH2F *hh = new TH2F("hh","hh",20,-800,800,20,-800,800);
	int total = pmvz->GetEntries();
	int steps = step > 0 ? total/step : 100;
	int start = 0;
	for(int i=0;i<steps;i++)
	{
//		pmvz->Draw("y:x>>h(20,-800,800,20,-800,800)","","",size,start);
      pmvz->Draw("y:x>>hh","","box",size,start);
		TH2F *h = (TH2F *)gPad->FindObject("h");
		gPad->Modified();
		gPad->Update();
		gSystem->Sleep(sleep);
		gSystem->ProcessEvents();
		start += step;
	}
}