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: Wrong Answer)

import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 文字列の入力
		String s = sc.next();
		String s1 = s.substring(0,1);
      	String s2 = s.substring(1,2);
      	String s3 = s.substring(2,3);
      	String s4 = s.substring(3,4);
      
      	if(s1.equals(s2) && s3.equals(s4)){
          if(!(s1.equals(s3))){
            System.out.println("Yes");
          }
        }else if(s1.equals(s3) && s2.equals(s4)){
          if(!(s1.equals(s2))){
            System.out.println("Yes");
          }
        }else if(s1.equals(s4) && s2.equals(s3)){
          if(!(s1.equals(s2))){
            System.out.println("Yes");
          }
        }else{
          System.out.println("No");
        } 
	}
}