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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.*;

public class Main {
	  public static void main(String args[]){
      	Scanner scan = new Scanner(System.in);
            
        String S = scan.next();
        String cnt;
        
        //パターンはOOXX,OXOX,OXXOの3パターンで文字が同じか調べればよいだけ
        
        if(S.substring(0,1).charAt(0) == S.substring(1,2).charAt(0) &&
          S.substring(2,3).charAt(0) == S.substring(3,4).charAt(0))
          cnt = "Yes";
        else if(S.substring(0,1).charAt(0) == S.substring(2,3).charAt(0) &&
          S.substring(1,2).charAt(0) == S.substring(3,4).charAt(0))
          cnt = "Yes";
        else if(S.substring(0,1).charAt(0) == S.substring(3,4).charAt(0) &&
          S.substring(1,2).charAt(0) == S.substring(2,3).charAt(0))
          cnt = "Yes";
        else
          cnt = "No";
        
        if(S.substring(0,1).charAt(0) == S.substring(1,2).charAt(0) &&
           S.substring(1,2).charAt(0) == S.substring(2,3).charAt(0) &&
           S.substring(2,3).charAt(0) == S.substring(3,4).charAt(0) )
          cnt = "No";
            
        System.out.println(cnt);
	  }
}