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: Accepted)

<?php 
fscanf(STDIN, "%s", $s);
  $array = str_split($s);
  if($array[0] === $array[1] && $array[2] === $array[3] && $array[1] !== $array[2]){
      echo 'Yes';
  }elseif($array[0] === $array[2] && $array[1] === $array[3] && $array[0] !== $array[1]){
      echo 'Yes';
  }elseif($array[0] === $array[3] && $array[1] === $array[2] && $array[0] !== $array[1]){
      echo 'Yes';
  }else{
      echo 'No';
  }
  ?>