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: Wrong Answer)

<?php
list($S)=sscanf(trim(fgets(STDIN)),"%s");
$S1 = substr($S,0,2);
$S2 = substr($S,-2);
if(($S[0] == $S[1])&&($S1 == $S2)){
    printf("No");
}
if($S1 == $S2){
    printf("Yes");
    exit;
}
if($S1 == strrev($S2)){
    printf("Yes");
    exit;
}
print("No");