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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
  $str = fgets(STDIN);
	$array = str_split($str);
	$uni = array_unique($array);
	if(count($uni) ==2) {
      $st_c1 = substr_count($uni[0],$str);
      if ($st_c1 == 2) {
        $st_c2 = substr_count($uni[1],$str);
      }
      $flg = $st_c1 == 2 && $st_c2 ==2 ? true : false;
    }
    echo $flg ? "Yes" :"No";
?>