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.Scanner;
class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        
        char S1 = str.charAt(0);
        char S2 = str.charAt(1);
        char S3 = str.charAt(2);
        char S4 = str.charAt(3);

        String result = null;
        // if (S1 == S2) {
        //     if (S3 == S4) System.out.println("Yes");
        // } else if (S1 == S3) {
        //     if (S2 == S4) System.out.println("Yes");
        // } else if (S1 == S4) {
        //     if (S2 == S3) System.out.println("Yes");
        // } else {
        //     System.out.println("No");
        // }

        if (S1 == S2) {
            result = (S3 == S4) ? "Yes" : "No";
        } else if (S1 == S3) {
            result = (S2 == S4) ? "Yes" : "No";
        } else if (S1 == S4) {
            result = (S2 == S3) ? "Yes" : "No";
        } else {result = "No";}
        System.out.println(result);
    }
}