void addhisto(){
  TH2* hist = new TH2F("herr_dipAngle_stt","",200,-0.05,0.05,10,0,10);
  std::ifstream listroot("reco.txt");
  string filename;
  
  if(listroot.is_open()){
    while(listroot){
      std::getline(listroot,filename);
      
      TFile* f1 = new TFile(filename.c_str());
      TH2* histo = (TH2F*)f1->Get("herr_dipAngle_stt");
      
      hist->Add(histo);
    }
  }
  
  TFile* outfile = new TFile("th2out.root","recreate");
  hist->Write();
  outfile->Close();
}