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

    $s = trim(fgets(STDIN));
    $count = 0;
   for($i=0;$i<strlen($s);$i++){
       if(substr_count($s,$s[$i]) <= 1){
           $count ++;
       }
   }
    if($count >0){
        echo "No\n";
    }else{
        echo "Yes\n";
    }