PROGRAM	classwat

c	List waters by numbers of H-bonding main chain partners

	CHARACTER*66	line(12000), wat(240), junk
	INTEGER		num(240)/240*0/, hist(0:6)/7*0/
	REAL		x(3), z(3)

	WRITE (6, 1000) 'Enter distance criterion:'
	READ (5, 999) crit
999	FORMAT (4f10.4)
	crit = crit*crit

	OPEN (unit=1, file='PCDall.pdb', status='OLD', readonly)
	n = 0
	DO WHILE (.TRUE.)
1	  READ (1, 1000, end=9) junk
1000	  FORMAT (a, f8.3)
	  IF (junk(18:20) .EQ. 'WAT') THEN
	    IF (junk(22:22) .EQ. 'A') THEN
	      READ (junk(23:26),1001) nres
1001	      FORMAT (i4)
	      wat(nres-600) = junk
	    endIF
	    GOTO 1
	  endIF
	  IF (junk(14:17) .EQ. 'N   ' .OR. junk(14:17) .EQ. 'O   ') THEN
	    n = n + 1
	    IF (n .GE. 12000) WRITE (6, 1000) junk
	    line(n) = junk
	  endIF
	endDO
9	CLOSE (unit=1)
	nl = n

c	Count interactions

	DO i = 1,239
	  WRITE (6, 1000) wat(i)
	  READ (wat(i)(31:54), 1002) x
1002	  FORMAT (3f8.3)
	  DO j = 1,nl
	    READ (line(j)(31:54), 1002) z
	    dd = (x(1)-z(1))**2 + (x(2)-z(2))**2 + (x(3)-z(3))**2
	    IF (dd .LE. crit) THEN
	      num(i) = num(i) + 1
	      WRITE (6, 1000) line(j), SQRT(dd)
	    endIF
	  endDO
	  WRITE (6, 1000)
	endDO

c	Make histogram

	DO i = 1,239
	  hist(num(i)) = hist(num(i))+1
	endDO

	WRITE (6, 1003) (i, i=0,6)
1003	FORMAT (7i5)
	WRITE (6, 1003) (hist(i), i=0,6)
	end