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
$s = trim(fgets(STDIN));
$s = str_replace(array("\r\n","\r","\n"), '', $s);
$s = explode(" ", $s);

$S = $s[0];

$chars = array();
for ($i = 0; $i < 4; $i++) {
    $c = $S[$i];
    if (!isset($chars[$c])) {
        $chars[$c] = 0;
    }
    $chars[$c]++;
}

$ret = "Yes";
foreach ($chars as $char) {
    if ($char != 2) {
        $ret = "No";
        break;
    }
}

echo($ret);