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 PHP (5.6.30) (judge verdict: Accepted)

<?php
  $str = trim(fgets(STDIN));
  $input = str_split($str);
  $s1 = $input[0];
  $s2 = "";
  $c1 = 1;
  $c2 = 0;
  for($i=1;$i<4;$i++){
  	if($input[$i]!=$s1){
      $s2 = $input[$i];
    }
  }
  for($i=1;$i<4;$i++){
  	if($input[$i]==$s1){
      $c1++;
    }elseif($input[$i]==$s2){
      $c2++;
    }
  }

  if($c1==2 and $c2==2){
	echo("Yes");
  }else{
    echo("No");
  }