TCanvas *c1 = new TCanvas("cn","cn",50,50,800,600);
#include <TCanvas.h>
#include <TBox.h>
#include <TPave.h>
#include <TFrame.h>
#include <TFile.h>
#include <TTree.h>
#include <TROOT.h>
#include <TH1.h>
#include <TH2.h>
#include <TSystem.h>
#include <vector>
#include <TLorentzVector.h>
#include <math.h>
#include "TMath.h"
#include <iostream>
#include <fstream>
#include <algorithm>
#include <map>
#include <TFileMerger.h>

void stack_z_try()

{
 TFile *f1 = new TFile ("/afs/cern.ch/work/n/nmajeed/private/CMSSW_7_3_0/my_work/ttbar/tt_final_new.root");
 TFile *f2 = new TFile ("/afs/cern.ch/work/n/nmajeed/private/CMSSW_7_3_0/my_work/WZ/wz_fi.root");
 TFile *f3 = new TFile ("/afs/cern.ch/work/n/nmajeed/private/CMSSW_7_3_0/my_work/Tqz/tqz_final_new.root");
 TFile *f4 = new TFile ("/afs/cern.ch/work/n/nmajeed/private/CMSSW_7_3_0/my_work/DY/dy_fi_new.root");

 TH1D *z_ttbar = (TH1D*)f1->Get("Z_Inv_mass"); 
 TH1D *z_wz = (TH1D*)f2->Get("Z_Inv_mass");
 TH1D *z_tqz = (TH1D*)f3->Get("Z_Inv_mass");
 TH1D *z_dy = (TH1D*)f4->Get("Z_Inv_mass");

 z_ttbar->GetXaxis()->SetRangeUser(60,120);
 z_wz->GetXaxis()->SetRangeUser(60,120);
 z_tqz->GetXaxis()->SetRangeUser(60,120);
 z_dy->GetXaxis()->SetRangeUser(60,120);

 
 int r=1;
 z_ttbar->Rebin(r);
 z_wz->Rebin(r);
 z_tqz->Rebin(r);
 z_dy->Rebin(r);

  z_ttbar->SetLineColor(kBlack);
  z_ttbar->SetFillColor(kCyan+3);

  z_wz->SetLineColor(kBlack);
  z_wz->SetFillColor(kOrange+7);

  z_tqz->SetLineColor(kBlack);
  z_tqz->SetFillColor(kOrange);

  z_dy->SetLineColor(kBlack);
  z_dy->SetFillColor(kRed);

 THStack *hs = new THStack("hs","");

 hs->Add(z_ttbar);
 hs->Add(z_wz);
 hs->Add(z_tqz);
 hs->Add(z_dy);
 hs->GetXaxis()->SetRangeUser(60.,120.);
 hs->Draw("HIST");

 TLegend *leg = new TLegend( 0.6449843,0.65038,0.8377743,0.8838219,NULL,"brNDC");
 leg->SetFillColor(0);
 leg->SetBorderSize(0);
 leg->SetTextFont(42);
 leg->SetTextSize(0.03);
 leg->SetLineColor(1);
 leg->SetLineStyle(1);
 leg->SetLineWidth(1);
 leg->SetMargin(0.44);
 leg->SetNColumns(2);
 leg->SetColumnSeparation(.4);

 leg->AddEntry(z_ttbar,"t#bar{t}","f");
 leg->AddEntry(z_wz,"WZJets","f");
 leg->AddEntry(z_tqz,"tZq","f");
 leg->AddEntry(z_dy,"dy","f");
 leg->Draw();

 TLatex *   tex1 = new TLatex(0.836,0.936,"#sqrt[]{s}=13TeV, L_{int}= 36 fb^{-1}");
 tex1->SetNDC();
 tex1->SetTextAlign(31);
 tex1->SetTextFont(42);
 tex1->SetTextSize(0.042);
 tex1->SetLineWidth(2);
 tex1->Draw();

 TLatex * tex3 = new TLatex(0.25,0.936," Z Invariant mass");
 tex3->SetNDC();
 tex3->SetTextAlign(10);
 tex3->SetTextFont(52);
 tex3->SetTextSize(0.05);
 tex3->SetLineWidth(2);
 tex3->Draw();

c1->SaveAs("z_invariant_mass_changes.pdf");

}