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: Wrong Answer)

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

(defsolver solution-aaa ()
  (let ((l))
    (dotimes (i 4)
      (let* ((c (read-char))
	     (old (rassoc c l :test #'char=)))
	(push (cons (if old (1+ (car old)) 1)
		    c)
	      l)))
    (format t "~:[No~;Yes~]"
	    (= 2 (apply #'max
		   (mapcar #'car l))))))

(solution-aaa)