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
fscanf(STDIN, '%s', $s);
$ans = '';
if($s[0] == $s[1] && $s[2] == $s[3]) $ans = 'Yes';
elseif($s[0] == $s[2] && $s[1] == $s[3]) $ans = 'Yes';
elseif($s[0] == $s[3] && $s[1] == $s[2]) $ans = 'Yes';
else {
    $ans = 'No';
}
echo $ans, PHP_EOL;