program read_from_a_file 
         implicit none
         integer n, i
         real a
         write(*,*) "Opening file 'data.dat'... "
         open (unit=20 ,file='data.dat',status='OLD')
         open (unit=30 ,file='data2.dat')
         read(20,*) n
         write(30,*)n 
         write(*,*) "N data, square-rooting numbers from date.dat ..."
         do i = 1, n
           read(20,*) a
           a = sqrt(a)
           write(30,*) a
         end do
         close(20)
         close(30)
         write(*,*)"Results now sabed in 'data2,dat'." 
         end