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

$stdin = fopen('php://stdin', "r");
fscanf($stdin, "%s", $str);
$arr = str_split($str);
sort ($arr);
if ($arr[0] != $arr[2] && $arr[0] == $arr[1] && $arr[2] == $arr[3]) {    
    echo "Yes\n";
} else {
    echo "No\n";
}