double xmin =  99999.; // X axis minimum
double xmax = -99999.; // X axis maximum
double bw = 2.;        // bin width
TH1D *h;

void ComputeMinMax(TString filename)
{
   ifstream inp;
   double x,y;
   inp.open(filename.Data());
   while (inp >> x >> y) {
      if (x>0) {
         if (x<xmin) xmin = x;
         if (x>xmax) xmax = x;
      }
   }
}


void FillHistoFromFile(TString filename)
{
   ifstream inp;
   double x,y;
   inp.open(filename.Data());
   while (inp >> x >> y) {
      if (x>0) h->Fill(x,y);
   }
   inp.close();
}

void DumpHistogram()
{
   ofstream outp;
   double x,y;
   outp.open("result.txt");
   int n = h->GetNbinsX();
   for (int i; i<=n; i++) {
     outp << h->GetBinCenter(i) << " " << h->GetBinContent(i) << endl;
   }
   outp.close();
}

void khallod() {
   ComputeMinMax("Data1.txt");
   ComputeMinMax("Data2.txt");

   int nb = (xmax-xmin)/bw;
   h = new TH1D("h","h title",nb,xmin-bw/2.,xmax+bw/2.);
   h->GetXaxis()->SetTitle("Energy (keV)");
   h->GetYaxis()->SetTitle("Count");

   FillHistoFromFile("Data1.txt");
   FillHistoFromFile("Data2.txt");

   h->Draw("hist");
   DumpHistogram();
}