TH1F medialetture(char* nomefile, int N) {
  ifstream f(nomefile);
  TH1F istogramma("medie","Medie",300,-1.,2.);
  double xm=0, x=0;
  int i=0;
  while ( f.good() ) {
    f >> x;
    if ( f.eof() ) break;
    i++;
    xm+=x;
    if ( i==N ) {
      istogramma.Fill(xm/N);
      xm=0;
      i=0;
    }
  }
  f.close();
  return istogramma; 
}