program input1
implicit none
integer:: istat=0, i=0, num=0
character*20:: fname
real::x
real, dimension(:), allocatable::y
   print *,'input filename'
   read(unit=*,fmt='(A)')fname
   open(unit=2,file= fname,status='old')
    do while (istat == 0)
      i=i+1
      read(unit=2,fmt=*,iostat=istat)x
   end do  
   num = i-1
   rewind(unit=2)
   allocate (y(1:num))
   print*,'there are ',num,' values in the file'
   print *,'y values:'
   do i=1,num 
      read(unit=2,fmt=*)y(i) 
      print *,y(i)
   end do
   deallocate(y)
end program  input1