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: Runtime Error)

<?php
  $s = trim(fgrts(STDIN));
  
  $tmp = [];
  for($i=0; $i<4; $i++){
    $tmp[$s[$i]] = isset($tmp[$s[$i]]) ? $tmp[$s[$i]]++ : 1;
  }

  $flag = true;
  if(count($tmp)==2){
    foreach($tmp as $num){
      if($num!=2){
        $flag = false;
        break;
      }
    }
  }else{
    $flag = false;
  }

  echo $flag ? "Yes\n" : "No\n";