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 (7.4.4) (judge verdict: Wrong Answer)

<?php
fscanf(STDIN, "%s", $s);
$s_1 = substr($s, 0, 1);
$s_2 = substr($s, 1, 1);
$s_3 = substr($s, 2, 1);
$s_4 = substr($s, 3, 1);

if ($s_1 === $s_2 && substr_count($s, $s_1) === 2 && substr_count($s, $s_2) === 2) {
    echo 'Yes';
} elseif ($s_1 === $s_3 && substr_count($s, $s_1) === 2 && substr_count($s, $s_3) === 2) {
    echo 'Yes';
} elseif ($s_1 === $s_4 && substr_count($s, $s_1) === 2 && substr_count($s, $s_4) === 2) {
    echo 'Yes';
} elseif ($s_3 === $s_2 && substr_count($s, $s_3) === 2 && substr_count($s, $s_2) === 2) {
    echo 'Yes';
} else {
    echo 'No';
}