program read_n_find_max
      character*20 fname
      write(*,*)'Which file to read data?(20 chr)'
      read(*,*) fname
      open(unit=12,file=fname)
c     open(unit=12,file=fname,status='old')
      read(12,*)n
      write(*,*) 'There are',n,'data points in your file.'
      read(12,*)a
      a_max = a 
      do i=2,n
        read(12,*)a
        if(a > a_max) a_max = a
      end do
c     close(12)
      write(*,*)'The maximum is :',a_max
      end