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 s = sc.next();
    
    String a = s.substring(0, 1);
    String b = s.substring(1, 2);
    String c = s.substring(2, 3);
    String d = s.substring(3, 4);
    
    if (a.equals(b) && b.equals(c) && c.equals(d)) {
      System.out.println("No");
    } else if (a.equals(b) && c.equals(d)) {
      System.out.println("Yes");
    } else if (a.equals(c) && b.equals(d)) {
      System.out.println("Yes");
    } else if (a.equals(d) && b.equals(c)) {
      System.out.println("Yes");
    } else {
      System.out.println("No");
    }
  }
}