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 (5.6.30) (judge verdict: Wrong Answer)

<?php
$ant_arr = trim(fgets(STDIN));

$ans = [];

for ($i = 0; $i < 4; ++$i) {
    if (count($ans) > 2) {
        echo "No\n";
        return;
    }
    
    if (!in_array($ant_arr[$i], $ans)) {
        $ans[] = $ant_arr[$i];
    }
}

echo "Yes\n";