program checkx
      implicit none
      integer*4 i,nat,ni,nj,mi,mj,j,is,iargc
      real*8 x,y,z,r,rmin,rmax
      real*8,allocatable::xx(:),yy(:),zz(:)
      integer*4,allocatable::it(:)
      character*80 fn
      write(6,*)'Checks atom distances in .x file'
      if(iargc().ne.1)then
       write(6,*)'Usage: checkx <filename>'
       stop
      endif
      call getarg(1,fn)
      open(9,file=fn)
      read(9,*)
      read(9,*)nat
      allocate(it(nat),xx(nat),yy(nat),zz(nat))
      do 1 i=1,nat
   1  read(9,*)it(i),xx(i),yy(i),zz(i)
      close(9)
      write(6,*)nat,' atoms'
      is=0
      ni=1
      nj=1
      mi=1
      mj=1
      if(nat.lt.2)stop
      rmin=1.0d9
      rmax=0.0d0
      do 2 i=1,nat
      x=xx(i)
      y=yy(i)
      z=zz(i)
      do 2 j=i+1,nat
      r=dsqrt((x-xx(j))**2+(z-zz(j))**2+(y-yy(j))**2)
      if(r.gt.rmax)then
       rmax=r
       mi=i
       mj=j
      endif
      if(r.lt.rmin)then
       rmin=r
       ni=i
       nj=j
      endif
      if(r.lt.0.5d0)then
       is=is+1
       write(6,601)i,it(i),j,it(j),r
601    format(' Small distance:',2(i6,'(',i6,')'),f12.6,' !')
      endif
   2  continue
      write(6,600)mi,it(mi),mj,it(mj),rmax,ni,it(ni),nj,it(nj),rmin
600   format(' Maximum distance:',2(i6,'(',i6,')'),f12.6,/,
     1       ' Minimum distance:',2(i6,'(',i6,')'),f12.6,/)
      if(is.gt.0)write(6,602)is
602   format(i6,' small distancies')
      end