void readDigits(){

  gSystem->Load("libITSUpgradeBase");
  gSystem->Load("libITSUpgradeSim");
  gROOT->SetStyle("Plain");

  const Int_t nLayers = 6;
  Int_t nbins=100;
  Int_t xmin=0;
  Int_t xmax=50000;//00*1e-09;


  TH1D *hNelSDig[nLayers], *hNelDig[nLayers];
  for(Int_t i=0; i< nLayers; i++ ) {
    hNelSDig[i] = new TH1D(Form("hNelSDig%i",i),Form("electron distribution in SDigits [ Layer %i] ",i),nbins,xmin,xmax);
    hNelSDig[i]->SetXTitle("N electrons");
    hNelDig[i] = new TH1D(Form("hNelDig%i",i),Form("electron distribution in Digits [ Layer %i] ",i),nbins,xmin,xmax);
    hNelDig[i]->SetXTitle("N electrons");
  }

  const Int_t layers = 6;

  gAlice=NULL;
  AliRunLoader* runLoader = AliRunLoader::Open("galice.root");
  runLoader->LoadgAlice();

  gAlice = runLoader->GetAliRun();

  runLoader->LoadHeader();
  runLoader->LoadKinematics();
  runLoader->LoadSDigits();
  runLoader->LoadDigits();

  AliLoader *dl = runLoader->GetDetectorLoader("ITS");


  //SDIGITS INIT
  TTree * sDigTree = 0x0;
  TObjArray *sDigList= new TObjArray(layers);
  for(Int_t i=0; i<layers; i++) sDigList->AddAt(new TClonesArray("AliITSDigitUpgrade"),i);

  //DIGITS INIT
  TTree * digTree = 0x0;
  TObjArray *digList= new TObjArray(layers);
  for(Int_t i=0; i<layers; i++) digList->AddAt(new TClonesArray("AliITSDigitUpgrade"),i);

  printf("N Events : %i \n",(Int_t)runLoader->GetNumberOfEvents());

  for (Int_t iEvent = 0; iEvent < runLoader->GetNumberOfEvents(); iEvent++) {
    printf("\n Event %i \n",iEvent);
    runLoader->GetEvent(iEvent);
    AliStack *s = runLoader->Stack();
    sDigTree=dl->TreeS();
    digTree=dl->TreeD();

    for(Int_t ilayer=0; ilayer<layers; ilayer ++) {
      digTree->SetBranchAddress(Form("Layer%d",ilayer),&(*digList)[ilayer]);
      sDigTree->SetBranchAddress(Form("Layer%d",ilayer),&(*sDigList)[ilayer]);
    }

    // LOOPS
 
    digTree->GetEntry(0);
    sDigTree->GetEntry(0);

    for(Int_t il=0; il<layers; il++){
      TClonesArray *pArrDig= (TClonesArray*)digList->At(il);
      TClonesArray *pArrSdig= (TClonesArray*)sDigList->At(il);
      for(Int_t isdentry=0;  isdentry< pArrSdig->GetEntries(); isdentry++) {
	AliITSDigitUpgrade *pSdig = (AliITSDigitUpgrade*)pArrSdig->At(isdentry);
	cout << " --- SDigit generated by a "<<s->Particle(pSdig->GetTrack(0))->GetName()<<"----"<<endl;
	hNelSDig[pSdig->GetLayer()]->Fill(pSdig->GetNelectrons()); 
	pSdig->PrintInfo();
      }

      for(Int_t ientry=0;  ientry< pArrDig->GetEntries(); ientry++) {
	cout << " --- Digit ---"<<endl;
	AliITSDigitUpgrade *pDig = (AliITSDigitUpgrade*)pArrDig->At(ientry); 
	hNelDig[pDig->GetLayer()]->Fill(pDig->GetNelectrons()); 
	pDig->PrintInfo();
      }
    }

  }//event loop
  TCanvas *cSd = new TCanvas("cSd","Summable Digits",1000,800);
  cSd->Divide(3,2);
  TCanvas *cD = new TCanvas("cD","Digits",1000,800);
  cD->Divide(3,2);

  for(Int_t ip =1; ip<=6; ip++){
    cSd->cd(ip);
    hNelSDig[ip-1]->Draw();
    cD->cd(ip);
    hNelDig[ip-1]->Draw();
  }


}