program xshell_express
      implicit none
      integer*4 n1,nat,nm,is,i,ii,j,k,im,jj,imm,jm
      integer*4 ,allocatable::as(:),asn(:)
      real*8,allocatable::r(:,:),rn(:,:)
      real*8 rmax,anm,cm(3),x,y,z
      character*20 st
      character*80 s80
      if(iargc().ne.3)then
       write(6,*)'Usage: xshell_express rlim n1 nm'
       stop
      else
       call getarg(1,st)
       read(st,*)rmax
       write(6,602)rmax
602    format(' Cut-off distance:',f8.2,' A')
       call getarg(2,st)
       read(st,*)n1
       call getarg(3,st)
       read(st,*)nm
      endif
      rmax=rmax*rmax
      anm=dble(nm)
      open(3,file='FILE.X',status='old')
      read(3,*)
      read(3,*)nat
      close(3)
      allocate(as(nat),r(nat,3),asn(nat),rn(nat,3))

      is=0
      imm=0
      open(3,file='FILE.X',status='old')
      open(33,file='RFILE.X')
1     read(3,300,end=999,err=999)s80
300   format(a80)
      read(3,*,end=999,err=999)nat
      is=is+1
      im=0
      do 2 i=1,nat
2     read(3,*)as(i),(r(i,k),k=1,3)
c     first n1 atoms automatically:
      do 3 i=1,n1
      asn(i)=as(i)
      do 3 k=1,3
3     rn(i,k)=r(i,k)
      ii=n1
c     inspect the molecules:
      jm=0
      do 4 i=n1+1,nat-nm+1,nm
      im=im+1
      do 51 k=1,3
      cm(k)=0.0d0
      do 5 j=i,i+nm-1
5     cm(k)=cm(k)+r(j,k)
51    cm(k)=cm(k)/anm
      do 6 j=1,n1
      x=r(j,1)
      y=r(j,2)
      z=r(j,3)
      if((x-cm(1))**2+(y-cm(2))**2+(z-cm(3))**2.lt.rmax)then
       do 7 jj=i,i+nm-1
       ii=ii+1
       asn(ii)=as(jj)
       do 7 k=1,3
7      rn(ii,k)=r(jj,k)
       jm=jm+1
       goto 4
      endif
6     continue
4     continue
      write(33,300)s80
      write(33,*)ii
      do 8 i=1,ii
8     write(33,333)asn(i),(rn(i,k),k=1,3)
333   format(i6,3f12.6)
      if(jm.gt.imm)imm=jm
      goto 1
999   close(3)
      close(33)

      write(6,6003)is,im,imm
6003  format(/,i4,' structures, ',i3,' molecules,',i4,' maximum left')
      end