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 sc = new Scanner(System.in);
      String str = sc.next();
      String a1 = str.substring(0,1);
      String a2 = str.substring(1,2);
      String a3 = str.substring(2,3);
      String a4 = str.substring(3,4);
      if(a1.equals(a2) && a3.equals(a4) && !(a1.equals(a3))) System.out.println("Yes");
      else if(a1.equals(a3) && a2.equals(a4) && !(a1.equals(a2))) System.out.println("Yes");
      else if(a1.equals(a4) && a2.equals(a3) && !(a1.equals(a2))) System.out.println("Yes");
      else System.out.println("No");
    }
}