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 Perl (v5.18.2) (judge verdict: Wrong Answer)

$inline = <>;
chomp($inline);

@array = split(//, $inline);
foreach $xx (@array){
	if($box{$xx} eq ""){
    	$box{$xx} = 1;
    }else{
    	$box{$xx}++;
    }
}

@keylist = keys(%box);
if($#keylist != 1){
	print "No\n";
}

$flag = 0;
foreach $xx (@keylist){
	if($box{$xx} != 2){
    	$flag = 1;
    }
}
if($flag == 0){
	print "Yes\n";
}else{
	print "No\n";
}