Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

(defmacro defsolver (name vars &body body)
  `(defun ,name ()
     (let (,@(mapcar #'list
            vars
            (mapcar (constantly '(read))
                vars)))
       ,@body)))

(defsolver solution-a ()
  (let* ((l (loop repeat 4 collect
		 (read-char))))
    (format t "~:[No~;Yes~]"
	    (and
	     (not
	      (and
	       (eql (nth 0 l) (nth 1 l))
	       (eql (nth 2 l) (nth 1 l))
	       (eql (nth 3 l) (nth 1 l))))
	     (or
	      (and
	       (eql (nth 0 l) (nth 1 l))
	       (eql (nth 2 l) (nth 3 l)))
	      (and
	       (eql (nth 0 l) (nth 2 l))
	       (eql (nth 1 l) (nth 3 l)))
	      (and
	       (eql (nth 0 l) (nth 3 l))
	       (eql (nth 1 l) (nth 2 l))))))))

(solution-a)