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 java.util.Scanner(System.in);
        String s = scan.next();
        boolean b = false;
        if(s.charAt(0) == s.charAt(1) && s.charAt(2) == s.charAt(3)){
            b = true;
        }else if(s.charAt(0) == s.charAt(2) && s.charAt(1) == s.charAt(3)){
            b = true;
        }else if(s.charAt(0) == s.charAt(3) && s.charAt(1) == s.charAt(2)){
            b = true;
        }
        if(s.charAt(0) == s.charAt(1) && s.charAt(1) == s.charAt(2) && s.charAt(2) == s.charAt(3)){
            b = false;
        }
        if(b){
            System.out.println("Yes");
        }else{
            System.out.println("No");
        }
    }
}