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

$a = trim(fgets(STDIN));
$b = strlen($a);
$input = str_split($a);
$result = "No";

if ((($input[0] == $input[1] && $input[2] == $input[3]) and ($input[2] != $input[1])) or
    ($input[0] == $input[2] && $input[1] == $input[3]) and ($input[0] != $input[1]) or
    ($input[0] == $input[3] && $input[2] == $input[1]) and ($input[0] != $input[1])) {
    $result = "Yes";
} else if ($input[0] == $input[1] && $input[0] == $input[2]) {
    $result = "No";
} else if ($input[0] == $input[1] && $input[0] == $input[3]) {
    $result = "No";
}
echo $result;
?>