{
    TFile *fin = new TFile("example_data.root");
    TNtupleD *nt = (TNtupleD *)fin->Get("nt");

    const double MEAN = 1.0;
    const double SIGMA = 0.05;
    
    int count_sigregion = 0, count_sideband = 0;
    for(int evt=0; evt<nt->GetEntries(); evt++) {
        nt->GetEntry(evt);
        double mass = nt->GetArgs()[0];
        
        if (fabs(mass-MEAN)<SIGMA*3.) count_sigregion++;
        if (fabs(mass-MEAN)>SIGMA*3.5 &&
            fabs(mass-MEAN)<SIGMA*6.5) count_sideband++;
    }
    
    double S = count_sigregion - count_sideband;
    double dS = sqrt(count_sigregion+count_sideband);
    printf("N(sig) = %.1f +- %.1f\n",S,dS);
}