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
$string = str_replace(array(" ", "\n"), "", fgets(STDIN));
$splited_string = str_split($string);
$counted_string = array_count_values($splited_string);
foreach ($counted_string as $count) {
  if ($count != 2) {
    echo "No";
    exit;
  }
}

echo "Yes";