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.nextLine();
    char c1 = S.charAt(0);
    char c2 = S.charAt(1);
    char c3 = S.charAt(2);
    char c4 = S.charAt(3);
    
    String ans = "No";
    if((c1 == c2 && c3 == c4 && c1 != c3) || (c1 == c3 && c2 == c4 && c1 != c2) || (c1 == c4 && c2 == c3 && c1 != c2)){
      ans = "Yes";
    }    
    System.out.println(ans);
  }
}