int test_output(string fname){
    TFile *f1 = new TFile(fname.c_str());
    TTree *E = (TTree*)f1->Get("E");
    if (E->GetEntries()==1000) {
            cout << "file is OK" << endl;
            return 0;
    } else {
            cerr << "file is not OK" << endl;
            return 1;
    }
}