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: Accepted)

<?php
$s = trim(fgets(STDIN));
$str = str_split($s);

for($i=0; $i<count($str); $i++){
    $result = array_keys($str, $str[$i]);
    if(count($result) != 2){
        echo "No";
        exit;
    }
}
echo "Yes";
?>